[Clang][Parser] Don't always destroy template annotations at the end of a declaration (#89494)

Since
[6163aa96](https://github.com/llvm/llvm-project/commit/6163aa96799cbad7f2f58e02c5bebee9647056a5#diff-3a7ef0bff7d2b73b4100de636f09ea68b72eda191b39c8091a6a1765d917c1a2),
we have introduced an optimization that almost always destroys
TemplateIdAnnotations at the end of a function declaration. This doesn't
always work properly: a lambda within a default template argument could
also result in such deallocation and hence a use-after-free bug while
building a type constraint on the template parameter.

This patch adds another flag to the parser to tell apart cases when we
shouldn't do such cleanups eagerly. A bit complicated as it is, this retains
the optimization on a highly templated function with lots of generic lambdas.

Note the test doesn't always trigger a conspicuous bug/crash even with a
debug build. But a sanitizer build can detect them, I believe.

Fixes https://github.com/llvm/llvm-project/issues/67235
Fixes https://github.com/llvm/llvm-project/issues/89127