Add support for boolean literals in macros (#6418)

Adding support for macros with boolean literals.

Demo:

```c++
// main.carbon

library "Main";

import Core library "io";

import Cpp inline '''
  #define M_TRUE true
''';

fn Run() -> i32 {
  let a: bool = Cpp.M_TRUE;
  if (a) {
    Core.Print(1);
  } else {
    Core.Print(0);
  }
  return 0;
}
```

```
$ bazel-bin/toolchain/carbon compile main.carbon
$ bazel-bin/toolchain/carbon link main.o \--output=demo_carbon
$ ./demo_carbon
1
```

Part of #6303

toolchain/check/cpp/import.cpp

@@ -2244,9 +2244,8 @@ static auto IsIncompleteClass(Context& context, SemIR::NameScopeId scope_id)
              context.classes().Get(class_decl->class_id).self_type_id);
 }
 
-// Maps a Clang literal expression to a Carbon constant. Currently supports
-// only integer and floating-point literals.
-// TODO: Add support for the other constant types for which a C++ to Carbon type
+// Maps a Clang literal expression to a Carbon constant.
+// TODO: Add support for all constant types for which a C++ to Carbon type
 // mapping exists.
 static auto MapConstant(Context& context, SemIR::LocId loc_id,
                         clang::Expr* expr) -> SemIR::InstId {
@@ -2286,6 +2285,13 @@ static auto MapConstant(Context& context, SemIR::LocId loc_id,
         context,
         MakeImportedLocIdAndInst<SemIR::IntValue>(
             context, imported_loc_id, {.type_id = type_id, .int_id = int_id}));
+  } else if (auto* bool_literal = dyn_cast<clang::CXXBoolLiteralExpr>(expr)) {
+    inst_id = AddInstInNoBlock(
+        context,
+        MakeImportedLocIdAndInst<SemIR::BoolLiteral>(
+            context, imported_loc_id,
+            {.type_id = type_id,
+             .value = SemIR::BoolValue::From(bool_literal->getValue())}));
   } else if (auto* float_literal = dyn_cast<clang::FloatingLiteral>(expr)) {
     FloatId float_id = context.floats().Add(float_literal->getValue());
     inst_id = AddInstInNoBlock(context,