[clang-format] Allow to set token types final

We have a little problem. TokenAnnotator::resetTokenMetadata() resets
the type, except for a (growing) whitelist. This is because the
TokenAnnotator visits some tokens multiple times. E.g. trying to
identify if a < is an operator less or a template opener. And in some
runs, which are bascially "reverted" the types are reset.

On the other hand, if the parser does already know the type, it should
be able to set it, without it being reset. So we introduce the ability
to set a type and make that final.

Differential Revision: https://reviews.llvm.org/D120511