[clang-tidy] Disable Checks on If constexpr statements in template...

[clang-tidy] Disable Checks on If constexpr statements in template Instantiations for BugproneBranchClone and ReadabilityBracesAroundStatements

Summary: fixes [[ https://bugs.llvm.org/show_bug.cgi?id=32203 | readability-braces-around-statements broken for if constexpr]] and [[ https://bugs.llvm.org/show_bug.cgi?id=44229 | bugprone-branch-clone false positive with template functions and constexpr ]] by disabling the relevant checks on if constexpr statements while inside an instantiated template. This is due to how the else branch of an if constexpr statement is folded away to a null statement if the condition evaluates to false

Reviewers: alexfh, hokein, aaron.ballman, xazax.hun

Reviewed By: aaron.ballman, xazax.hun

Subscribers: rnkovacs, JonasToth, Jim, lebedev.ri, xazax.hun, cfe-commits

Tags: #clang-tools-extra, #clang

Differential Revision: https://reviews.llvm.org/D71980