[llvm] Create a CharSetConverter class with both iconv and icu support (PR #74516)

[David Blaikie via llvm-commits]

dwblaikie wrote:

> Adding some more reviewers to cover cmake changes, packaging questions, and folks who expressed opinions on the RFC.

A link back to the RFC for those playing along at home: https://discourse.llvm.org/t/rfc-adding-a-charset-converter-to-the-llvm-support-library/69795

https://github.com/llvm/llvm-project/pull/74516