Add context to Media & Text block keyword 'half'

[Soean]

Describe the bug
Media & Text block introduced in 4.1., adds the keyword half. The german polyglots team wasn't able to translate the string because of missing context. So we should add a context.

[swissspidy]

I think it's we should remove that keyword entirely.

Looking at the code I have no idea what it means. Half media and half text? According to #9416 the block was referred to "half image layout" once. But that's not really useful for a user and not something I would actually type in to search for a media and text block.

[mtias]

I agree we should remove "half".