[clang] [clang][NFC] Refactor enums that hold size of `Type` and `DeclContext` bit-fields (PR #70296)

[Aaron Ballman via cfe-commits]

================
@@ -1739,10 +1734,8 @@ class DeclContext {
     uint64_t IsSimpleExplicit : 1;
   };
 
-  /// Number of non-inherited bits in CXXConstructorDeclBitfields.
-  enum {
-    NumCXXConstructorDeclBits = 64 - NumDeclContextBits - NumFunctionDeclBits
-  };
+  /// Number of inherited and non-inherited bits in CXXConstructorDeclBitfields.
+  enum { NumCXXConstructorDeclBits = 64 };
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AaronBallman wrote:

```suggestion
  enum { NumCXXConstructorDeclBits = NumFunctionDeclBits + 20 };
```
For consistency with others?

https://github.com/llvm/llvm-project/pull/70296