Fix l10n regex for unnamed percentages (#18514)
Fixup of #18503 and #18270
Summary of the issue:
The regex to check for unnamed string interpolations doesn't support the %% symbol, which escapes %.
This leads to certain usages of it raising incorrect interpolation errors.
File source/locale/tr/LC_MESSAGES/nvda.po: 1 error
Message starting on line 10286
Original: "%s%%"
Translated: "%%%s"
Error: unnamed percent interpolations differ
Expected: unnamed percent interpolations in this order: ['%s']
The regex for missing names for brace interpolations is not working.
i.e. "{}" should raise an error without a name like "{name}".
This causes issues where the order of the arguments change in the string.
e.g. "Character: {}\nReplacement: {}" being translated to "Replacement: {}\nCharacter: {}" will result in the expected interpolation being in the wrong place.
These should be fixed in the source .po files to add names to instances of "{}".
Description of user facing changes:
Adds a more rigourous check for interpolations using brace formats, which will reduce string errors in the UI.
