[clang] [clang][NFC] move traits to tablegen (PR #201491)

[Matthias Wippich via cfe-commits]

================
@@ -0,0 +1,556 @@
+class Trait<string P> {
+  string Prefix = P;
+  string Spelling = "";
----------------
Tsche wrote:

A very small number of traits have alternative spellings, ie 
```cpp
ALIAS("__is_literal_type", __is_literal, KEYCXX)
ALIAS("__is_same_as", __is_same, KEYCXX)
```

Should this be `list<string> Spellings` instead?

https://github.com/llvm/llvm-project/pull/201491