Share LLVM dialect metadata materialization through `ModuleTranslation`
so named metadata and metadata-as-value lowering use one conversion
path. Resolve metadata symbol references to functions, globals, aliases,
and ifuncs, and diagnose malformed required metadata before lowering.
Rename `MDFuncAttr` to `MDGlobalValueAttr` to reflect its support for
symbol-backed global values.
610a3105af