Allow comma as a decimal separator for SpinBox

[aXu-AP]

Fixes #80664
Add support for comma , as a decimal separator for SpinBox. This implementation allows for expressions like pow(2, 3) to be used as well. If you use comma to separate decimals, use semicolon ; to separate function parameters.
Change EditorSpinSlider behavior to match (currently EditorSpinSlider accepts commas but not expression with multiple parameters).

Caveats: As comma replacing is triggered only in absence of parentheses, there's some cases where replacing doesn't trigger even if it would still make sense for example (1 + 0,5) * 2. However, if user needs to write something more complex than what can be inputted via numpad they probably don't mind using dot for decimals. Newer version handles these cases too.
This is also a change to an existing Control, but I can't see anybody relying on input failing whenever commas are present.

Bugsquad edit: Fixes #81989

[Calinou]

Tested locally (rebased on top of master a278c1b), it works as expected.

[MewPurPur]

I have an implementation in #80541 which I think is better, even if a bit overkill. This implementation just checks for (s, while mine checks for functions so math stuff like (2 + 3,5) * 5 work still.

[aXu-AP]

Oh, I didn't see that! Good work. I just came up with a third option, which is elegant and handles even edge cases: What if we tried parsing the text and if parse fails then try replacing commas and reparse? I'm testing this rn (ie. waiting to build 😴).

[aXu-AP]

It seems that expression succeeds even if there is some commas just lying around - the rest just gets cut off (eg. 5,5 evaluates as 5). So my idea for checking for failed expression doesn't work out of the box.

Oh well, I think this is good enough, or use Mew's fancier version if you want to handle more cases 😀

[MewPurPur]

Awh, the idea sounded very good in practice. Maybe there's some way to find whether Expression needs to do some meddling to make the string valid, so after two fails it trims off the "invalid part"? I don't know if the functionality exists in practice

[aXu-AP]

It worked out in the end! I just needed to try first converting commas, then in case of failure parse again without conversion. Now I couldn't find any edge cases, seems to work in all (sensible) cases.
Also I added conversion from semicolons ; to commas ,. This is how we do it in Finland if we need to separate multiple decimal numbers. After quick googling it seems to be the standard for French and some other countries as well.

[MewPurPur]

Yay! This supersedes my PR beautifully then

[aXu-AP]

Rebased

[KoBeWi]

Seems fine, but seeing the duplicate code in EditorSpinSlider and SpinBox I wonder if maybe it should be a static SpinBox method, with text as a parameter?

[KoBeWi]

Apparently this also fixes #81989 (and consequently, supersedes #82020).

[YuriSizov]

Thanks!

[Crystalwarrior]

This problem came back in Godot 4.3 :/

[aXu-AP]

Can you elaborate? For me it seems to be working both in 4.3 and in master.