Fix + prefix handling in to_int/to_float utilities

[SiarheiFedartsou]

Please don't force-push once you received the first review.

Issue

#5704 (comment)

We also could add some special handling for − (not to be confused with -), but not sure we really should: I guess there are many variants of symbols which are similar to minus symbol, but not really minus - tbh not sure if we should handle them all in these utilities - may be it is better to make a part of some Lua preprocessing or something like this.

Tasklist

• Add tests
• Add #fixes with the issue number that this PR addresses
• Update the docs with any new request parameters or changes to behavior described
• Update the changelog
• If you made changes to the lua files, update the taginfo too
• If you made changes to a translation file, update transifex too

Requirements / Relations

Link any requirements here. Other pull requests this PR is based on?