[clang] Move const qualification of array to its elements (PR #131366)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

Non-canonical types, are, as the name suggests, non-canonical: they can have all kinds of type sugar, and type qualifiers at all levels.  Please don't try to change that; just fix getCommonSugaredType so it can tolerate a const qualifier in this position.

https://github.com/llvm/llvm-project/pull/131366