[clang] [clang]: implement std::meta::is_type (PR #211653)

[Ambrose Leeb via cfe-commits]

================
@@ -0,0 +1,35 @@
+/*===---- meta - header for reflection metafunctions -----------------------===
----------------
Sirraide wrote:

CC @philnik777 @ldionne for awareness that we’re adding this header in this patch. I believe we have talked about this before at some point, but we’re providing `<meta>` as part of Clang because of how much compiler magic and implementation-specific choices we’ll have to make, and because Clang simply will not be compatible w/ libstdc++’s `<meta>` header due to some of GCC’s implementation choices.

https://github.com/llvm/llvm-project/pull/211653