[clangd] Block clang-tidy misc-const-correctness check

This check performs an extremely large amount of work (for each variable, it
runs very many full matcher-driven traversals of the whole scope the variable
is defined in).

When (inadvertently) enabled for Fuchsia, it regressed BuildAST times by >10x
(400ms -> 7s on my machine).

Differential Revision: https://reviews.llvm.org/D135829