HsUniToken for :: in GADT constructors (#19623)

compiler/GHC/Parser.y

compiler/GHC/Parser/PostProcess.hs

compiler/GHC/Parser/PostProcess/Haddock.hs

compiler/GHC/Rename/Module.hs

compiler/GHC/ThToHs.hs

compiler/Language/Haskell/Syntax/Decls.hs

...e/tests/haddock/should_compile_flag_haddock/T17544.stderr

...ests/haddock/should_compile_flag_haddock/T17544_kw.stderr

testsuite/tests/parser/should_compile/DumpParsedAst.stderr

testsuite/tests/parser/should_compile/DumpRenamedAst.stderr

testsuite/tests/parser/should_compile/T15323.stderr

testsuite/tests/printer/T18791.stderr

utils/check-exact/ExactPrint.hs

utils/haddock