[clang-tidy] Abseil: faster strsplit delimiter check

This check is an abseil specific check that checks for code using single character string literals as delimiters and transforms the code into characters.

The check was developed internally and has been running at google, this is just
a move to open source the check. It was originally written by @sbenza.

Patch by Deanna Garcia!

llvm-svn: 340411