[test][libspirv] Add manually-generated tests for Rschar conversion built-ins#20920

wenju-he wants to merge 2 commits intointel:syclintel/llvm:syclfrom

wenju-he:libspirv-add-convert-Rschar-testswenju-he/llvm:libspirv-add-convert-Rschar-testsCopy head branch name to clipboard