std: update std.builtin.Type fields to follow naming conventions

The compiler actually doesn't need any functional changes for this: Sema
does reification based on the tag indices of `std.builtin.Type` already!
So, no zig1.wasm update is necessary.

This change is necessary to disallow name clashes between fields and
decls on a type, which is a prerequisite of #9938.

test/behavior/tuple_declarations.zig

@@ -10,7 +10,7 @@ test "tuple declaration type info" {
 
     {
         const T = struct { comptime u32 align(2) = 1, []const u8 };
-        const info = @typeInfo(T).Struct;
+        const info = @typeInfo(T).@"struct";
 
         try expect(info.layout == .auto);
         try expect(info.backing_integer == null);