[clang-tools-extra] [clangd] fix crashes in SemanticHighlighting on NTTP typed `decltype(constexpr-auto-variable)` (PR #207323)

[Nathan Ridge via cfe-commits]

HighCommander4 wrote:

> There is #42259

(That's an unrelated deficiency in the modeling of `auto` types which does not come into play here. In this case, both `getType()` and the TSI correctly contain deduced types, they just differ in the amount of type sugar they have.)

https://github.com/llvm/llvm-project/pull/207323