Add dumping for NamedConstraintId and shorten untagged id printing (#6319)

Adds support to the `dump` debugger command for named constraint ids,
which are printed as `constraint<number>`. While doing so, we print
whether the `constraint` is complete or not, and add the same to
`interface` to match.

And we noticed that the printing of name and name scope ids, which are
not tagged, are very verbose by adding 7 `0`s to them for no reason. So
make the dump output easier to read by dropping 0 prefixes.

Before:
```
name_scope00000000: {inst: inst0000000E, parent_scope: name_scope<none>, has_error: false, extended_scopes: [], names: {name00000000: inst6000000F, name00000001: inst60000011}} {kind: Namespace, arg0: name_scope00000000, arg1: inst<none>, type: type(inst(NamespaceType))} `package`
```

After:
```
name_scope0: {inst: instE, parent_scope: name_scope<none>, has_error: false, extended_scopes: [], names: {name0: inst6000000F, name1: inst60000011}} {kind: Namespace, arg0: name_scope0, arg1: inst<none>, type: type(inst(NamespaceType))} `package`
```

toolchain/base/shared_value_stores_test.cpp

@@ -52,13 +52,12 @@ TEST(SharedValueStores, PrintVals) {
   RawStringOstream out;
   value_stores.Print(out);
 
-  EXPECT_THAT(
-      Yaml::Value::FromText(out.TakeStr()),
-      MatchSharedValues(
-          ElementsAre(Pair("ap_int00000000", Yaml::Scalar("999999999999"))),
-          ElementsAre(Pair("real00000000", Yaml::Scalar("8*10^8"))), IsEmpty(),
-          ElementsAre(Pair("identifier00000000", Yaml::Scalar("a"))),
-          ElementsAre(Pair("string00000000", Yaml::Scalar("foo'\"baz")))));
+  EXPECT_THAT(Yaml::Value::FromText(out.TakeStr()),
+              MatchSharedValues(
+                  ElementsAre(Pair("ap_int0", Yaml::Scalar("999999999999"))),
+                  ElementsAre(Pair("real0", Yaml::Scalar("8*10^8"))), IsEmpty(),
+                  ElementsAre(Pair("identifier0", Yaml::Scalar("a"))),
+                  ElementsAre(Pair("string0", Yaml::Scalar("foo'\"baz")))));
 }
 
 }  // namespace