[clang-tidy] readability-identifier-naming.HungarianNotation: rename CharPrinter to CharPointer

The CharPrinter is a typo and should have been named CharPointer as it
configures the hungarian notation prefix for char pointers (char*).

As all configuration options within
readability-identifier-naming.HungarianNotation.CString.* were not read
at all in the previous clang-tidy version (fixed in D144431), this option
rename won't break existing users.

A note in release notes is added to let users know these options were
renamed.

Reviewed By: carlosgalvezp

Differential Revision: https://reviews.llvm.org/D144790