[clang][NFC] Remove const-qualification from...

[clang][NFC] Remove const-qualification from `FunctionTemplateSpecializationInfo::TemplateArguments` (#92500)

This patch remove const-qualification from pointee type of
`FunctionTemplateSpecializationInfo::TemplateArguments`, because it's
(eventually) used to initialize `MultiLevelTemplateArgumentList`, which
can actually mutate the arguments via

https://github.com/llvm/llvm-project/blob/f42f57b52dd279e6ae19270d063aeb8d59e3f11c/clang/include/clang/Sema/Template.h#L197-L204
Mutation seems to be required to correctly handle packs:

https://github.com/llvm/llvm-project/blob/9144553207052a868efc5a8ce61a0afbb0eaf236/clang/lib/Sema/SemaTemplateInstantiate.cpp#L1440-L1469