[clang-tidy] Handle template instantiations in container size check

readability-container-size-empty currently modifies source code based on
AST nodes in template instantiations, which means that it makes
transformations based on substituted types.  This can lead to
transforming code to be broken.

Change the matcher implementation to ignore template instantiations
explicitly, and add a matcher to explicitly handle template declarations
instead of instantiations.

Differential Revision: https://reviews.llvm.org/D91302