chore: improve translation string management

[philmoz]

Key changes:

• Cleanup string usage. Remove all direct usage of TR_xxx strings, always use STR_xxx version. Changes to the translation files no longer require re-compiling almost every other file.
• Add translation testing to tests build. Test all language translation files against the English base when running the 'tests' target. Issues with translation files can be caught during build.
• Remove conditional sections, and string array definitions from the translation files. This simplifies the files as each line is a single string to translate. Ensures string arrays always have the correct number of entries.
• Restructure 'translations' folder. Group translation and tts source files into sub folders. Move all translation related files into the translations folder.
• Easier addition of new strings. Edit a single file (string_list.h) instead of modifying multiple files.

Note: based on 3.0UI PR.