Add glossary check for source stings problematic in CSV

[nijel]

Describe the problem

Some strings can't be exposed in CSV to automatic translation backends (see #12791). Weblate should warn that these are problematic.

Describe the solution you would like

Add glossary only check to warn about using any of =+@- at the beginning of the string for both source and translation.

Describe alternatives you have considered

#12791 will deal with such strings, but these will be missing from the sync (or problematic characters stripped), so user should be notified of that.

Screenshots

No response

Additional context

Currently, no checks are triggered on glossary components:

weblate/weblate/trans/models/unit.py

Lines 1353 to 1355 in 64aa009

	if self.translation.component.is_glossary:
	# We might eventually run some checks on glossary
	checks = {}