[clang-tidy] Enhance modernize-use-auto to templated function casts

[clang-tidy] Enhance modernize-use-auto to templated function casts

Summary:
Use auto when declaring variables that are initialized by calling a templated
function that returns its explicit first argument.

Fixes PR26763.

Reviewers: aaron.ballman, alexfh, staronj, Prazek

Subscribers: Eugene.Zelenko, JDevlieghere, cfe-commits

Differential Revision: https://reviews.llvm.org/D27166

llvm-svn: 289797