[Clang] [NFC] Tablegen component diags headers (#134777)

The component diagnostic headers (i.e. `DiagnosticAST.h` and friends)
all follow the same format, and there’s enough of them (and in them) to
where updating all of them has become rather tedious (at least it was
for me while working on #132348), so this patch instead generates all of
them (or rather their contents) via Tablegen.

Also, it seems that `%enum_select` currently wouldn’t work in
`DiagnosticCommonKinds.td` because the infrastructure for that was
missing from `DiagnosticIDs.h`; this patch should fix that as well.

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