Allow template string symbols for vue files

[juliusknorr]

Properly extract translations from vue files that use ES6 template strings like:

return t(
	'accessibility',
	`Universal access is very important to us. We follow web standards
	and check to make everything usable also without mouse,
	and assistive software such as screenreaders.
	We aim to be compliant with the {guidelines} 2.1 on AA level,
	with the high contrast theme even on AAA level.`
)

Fixes nextcloud/server#14607