Propose new ClangIR Maintainer (#147365)

@xlauko is an active PR reviewer, contributing to ClangIR/MLIR
discussion for years now, and has been effectively overseeing the
quality of CIR dialect (the MLIR part). I'd like to nominate him to join
the list of maintainers.

---------

Co-authored-by: Henrich Lauko <xlauko@mail.muni.cz>

Author: bcardosolopes

clang/Maintainers.rst

@@ -59,6 +59,8 @@ Clang MLIR generation
 | Bruno Cardoso Lopes
 | bruno.cardoso\@gmail.com (email), sonicsprawl (Discord), bcardosolopes (GitHub)
 
+| Henrich Lauko
+| henrich.lau\@gmail.com  (email), henrich.lauko (Discord), xlauko (GitHub)
 
 Analysis & CFG
 ~~~~~~~~~~~~~~