Fix input width in MultiSelect UI components

[mikiher]

Fixes #2700 (see details in the bug).

Note that setInputWidth was removed, and with it the call to this.RecalcMenuPos().
I'm not sure why this call is required. If it is, let me know and I'll try to re-incorporate it where it makes sense.

[advplyr]

I'm not sure why I put the recalc there but I wrote that a long time ago so it may have gone through a few refactors. This is working great in my testing, thanks!

[mikiher]

Actually, I played with it a bit more today, and I'm not happy with my fix.

1. I examined in more detail what is the actual width after each letter is entered. It turns out that setting "width: fit-content" just sets a larger initial value for the width (163px, not sure how it's calculated), and it doesn't change at all when the input changes. It just seems like it works because of the larger initial width, but after you type enough, you only see the end of what you typed and the beginning is cut-off.
2. I think I now understand why recalcMenuPos is required - assuming width modification really works as expected, you could potentially have the inputWrapper div span more than one line, and the menu position needs to change when this happens.

I think I found another solution that requires less changes and really modifies the width.
Can you please revert the merge?

[mikiher]

OK, don't bother to revert, I'll just send a new PR