Make semir scope labels only print when non-empty (#6780)

This shifts logic a little so that empty top-level scopes are printed
less often. This affects imports mainly for now, but should be expected
to affect the soon-to-be-added generated scope more significantly.

Assisted-by: Google Antigravity with Gemini 3 Flash

toolchain/check/testdata/function/declaration/extern.carbon

@@ -227,9 +227,6 @@ extern library "basic" fn F();
 // CHECK:STDOUT:   %F: %F.type = struct_value () [concrete]
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: imports {
-// CHECK:STDOUT: }
-// CHECK:STDOUT:
 // CHECK:STDOUT: file {
 // CHECK:STDOUT:   package: <namespace> = namespace [concrete] {
 // CHECK:STDOUT:     .F = invalid

toolchain/check/testdata/function/declaration/extern_library.carbon

@@ -183,9 +183,6 @@ extern library "extern_library_owner" fn F() {}
 // CHECK:STDOUT:   %F: %F.type = struct_value () [concrete]
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: imports {
-// CHECK:STDOUT: }
-// CHECK:STDOUT:
 // CHECK:STDOUT: file {
 // CHECK:STDOUT:   package: <namespace> = namespace [concrete] {
 // CHECK:STDOUT:     .F = %F.decl
@@ -203,9 +200,6 @@ extern library "extern_library_owner" fn F() {}
 // CHECK:STDOUT:   %F: %F.type = struct_value () [concrete]
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: imports {
-// CHECK:STDOUT: }
-// CHECK:STDOUT:
 // CHECK:STDOUT: file {
 // CHECK:STDOUT:   package: <namespace> = namespace [concrete] {
 // CHECK:STDOUT:     .F = %F.decl
@@ -223,9 +217,6 @@ extern library "extern_library_owner" fn F() {}
 // CHECK:STDOUT:   %F: %F.type = struct_value () [concrete]
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: imports {
-// CHECK:STDOUT: }
-// CHECK:STDOUT:
 // CHECK:STDOUT: file {
 // CHECK:STDOUT:   package: <namespace> = namespace [concrete] {
 // CHECK:STDOUT:     .F = %F.decl
@@ -243,9 +234,6 @@ extern library "extern_library_owner" fn F() {}
 // CHECK:STDOUT:   %F: %F.type = struct_value () [concrete]
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: imports {
-// CHECK:STDOUT: }
-// CHECK:STDOUT:
 // CHECK:STDOUT: file {
 // CHECK:STDOUT:   package: <namespace> = namespace [concrete] {
 // CHECK:STDOUT:     .F = invalid
@@ -342,9 +330,6 @@ extern library "extern_library_owner" fn F() {}
 // CHECK:STDOUT:   %F: %F.type = struct_value () [concrete]
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: imports {
-// CHECK:STDOUT: }
-// CHECK:STDOUT:
 // CHECK:STDOUT: file {
 // CHECK:STDOUT:   package: <namespace> = namespace [concrete] {
 // CHECK:STDOUT:     .F = invalid

toolchain/check/testdata/function/declaration/extern_library_for_default.carbon

@@ -65,9 +65,6 @@ extern fn F();
 // CHECK:STDOUT:   %F: %F.type = struct_value () [concrete]
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: imports {
-// CHECK:STDOUT: }
-// CHECK:STDOUT:
 // CHECK:STDOUT: file {
 // CHECK:STDOUT:   package: <namespace> = namespace [concrete] {
 // CHECK:STDOUT:     .F = %F.decl
@@ -85,9 +82,6 @@ extern fn F();
 // CHECK:STDOUT:   %F: %F.type = struct_value () [concrete]
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: imports {
-// CHECK:STDOUT: }
-// CHECK:STDOUT:
 // CHECK:STDOUT: file {
 // CHECK:STDOUT:   package: <namespace> = namespace [concrete] {
 // CHECK:STDOUT:     .F = %F.decl

toolchain/check/testdata/function/declaration/extern_library_from_default.carbon

@@ -63,9 +63,6 @@ extern fn F();
 // CHECK:STDOUT:   %F: %F.type = struct_value () [concrete]
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: imports {
-// CHECK:STDOUT: }
-// CHECK:STDOUT:
 // CHECK:STDOUT: file {
 // CHECK:STDOUT:   package: <namespace> = namespace [concrete] {
 // CHECK:STDOUT:     .F = %F.decl
@@ -83,9 +80,6 @@ extern fn F();
 // CHECK:STDOUT:   %F: %F.type = struct_value () [concrete]
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: imports {
-// CHECK:STDOUT: }
-// CHECK:STDOUT:
 // CHECK:STDOUT: file {
 // CHECK:STDOUT:   package: <namespace> = namespace [concrete] {
 // CHECK:STDOUT:     .F = %F.decl

toolchain/check/testdata/function/declaration/fail_todo_no_params.carbon

@@ -176,13 +176,7 @@ fn A {
 // CHECK:STDOUT:
 // CHECK:STDOUT: --- fail_todo_arrow_body.carbon
 // CHECK:STDOUT:
-// CHECK:STDOUT: constants {
-// CHECK:STDOUT: }
-// CHECK:STDOUT:
 // CHECK:STDOUT: fn @A;
 // CHECK:STDOUT:
 // CHECK:STDOUT: --- fail_invalid_file_generic_regression_test.carbon
 // CHECK:STDOUT:
-// CHECK:STDOUT: constants {
-// CHECK:STDOUT: }
-// CHECK:STDOUT:

toolchain/check/testdata/function/declaration/implicit_import.carbon

@@ -91,9 +91,6 @@ extern fn A();
 // CHECK:STDOUT:   %A: %A.type = struct_value () [concrete]
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: imports {
-// CHECK:STDOUT: }
-// CHECK:STDOUT:
 // CHECK:STDOUT: file {
 // CHECK:STDOUT:   package: <namespace> = namespace [concrete] {
 // CHECK:STDOUT:     .A = %A.decl
@@ -131,9 +128,6 @@ extern fn A();
 // CHECK:STDOUT:   %A: %A.type = struct_value () [concrete]
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: imports {
-// CHECK:STDOUT: }
-// CHECK:STDOUT:
 // CHECK:STDOUT: file {
 // CHECK:STDOUT:   package: <namespace> = namespace [concrete] {
 // CHECK:STDOUT:     .A = %A.decl
@@ -168,9 +162,6 @@ extern fn A();
 // CHECK:STDOUT:   %A: %A.type = struct_value () [concrete]
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: imports {
-// CHECK:STDOUT: }
-// CHECK:STDOUT:
 // CHECK:STDOUT: file {
 // CHECK:STDOUT:   package: <namespace> = namespace [concrete] {
 // CHECK:STDOUT:     .A = %A.decl

toolchain/check/testdata/function/declaration/no_definition_in_impl_file.carbon

@@ -99,9 +99,6 @@ fn D();
 // CHECK:STDOUT:   %A: %A.type = struct_value () [concrete]
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: imports {
-// CHECK:STDOUT: }
-// CHECK:STDOUT:
 // CHECK:STDOUT: file {
 // CHECK:STDOUT:   package: <namespace> = namespace [concrete] {
 // CHECK:STDOUT:     .A = %A.decl.loc4
@@ -190,9 +187,6 @@ fn D();
 // CHECK:STDOUT:   %C: %C.type = struct_value () [concrete]
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: imports {
-// CHECK:STDOUT: }
-// CHECK:STDOUT:
 // CHECK:STDOUT: file {
 // CHECK:STDOUT:   package: <namespace> = namespace [concrete] {
 // CHECK:STDOUT:     .C = %C.decl