[clang-format] Fix formatting of struct-like records followed by variable declaration.

Fixes https://github.com/llvm/llvm-project/issues/24781.
Fixes https://github.com/llvm/llvm-project/issues/38160.

This patch splits `TT_RecordLBrace` for classes/enums/structs/unions (and other records, e.g. interfaces) and uses the brace type to avoid the error-prone scanning for record token.

The mentioned bugs were provoked by the scanning being too limited (and so not considering `const` or `constexpr`, or other qualifiers, on an anonymous struct variable declaration).

Moreover, the proposed solution is more efficient as we parse tokens once only (scanning being parsing too).

Reviewed By: MyDeveloperDay, HazardyKnusperkeks

Differential Revision: https://reviews.llvm.org/D119785