macos: expand set of string handling macros

As requested in the !1172 (merged) discussion, this introduces macros similar to those used in the Qt plugin (introduced in 6cd08480), which are ignored by the mechanism that scans for strings to be translated.

Additionally, in fixing this I happened to:

• Remove a duplicate null check in the macros.
• Fix a few cases of double translation lookups.
• Fix the few remaining cases not making use of the module_Get(Short|Long)Name() helpers.