[Lex] Avoid repeated hash lookups (NFC) (#107963)
MacroAnnotations has three std::optional fields.
Functions makeDeprecation, makeRestrictExpansion, and makeFinal
construct an instance of MacroAnnotations with one field initialized
with a non-default value (that is, some value other than
std::nullopt).
Functions addMacroDeprecationMsg, addRestrictExpansionMsg, and
addFinalLoc either create a new map entry with one field initialized
with a non-default value or replaces one field of an existing map
entry.
We can do all this with a simple statement of the form:
AnnotationInfos[II].FieldName = NonDefaultValue;
which takes care of default initialization of the fields with
std::nullopt when a requested map entry does not exist.
