StringUtil: Make TryParse of floats handle comma and dot decimal separators.

[jordan-woyak]

This should fix: https://bugs.dolphin-emu.org/issues/11899
(floats fail to parse on locales with non-dot decimal separators)

I also noticed signed integer and enum types were being handled by the overload intended for floats so I generalized the integer version of TryParse.

[AdmiralCurtiss]

This instead causes problems if someone has thousand-separators. Shouldn't we just force the C locale for config files?

[jordan-woyak]

@AdmiralCurtiss It looks like our "ToString" functions do not use thousand-separator format strings so this shouldn't be a problem.
I agree we should save in the "C" locale but we still need to handle loading of existing non-"C"-locale configs.

[JosJuice]

Yeah, I can't recall Dolphin ever writing thousands separators to config files.

[CookiePLMonster]

Decimal separators are rather rare I think and I'd be surprised if they were written in configs - for what it's worth, I think it's worth going as far as breaking some configs if it means achieving perfect consistency and making configs fully locale agnostic moving forward. It's a bit surprising they were following locales in the first place...

[JosJuice]

Decimal separators are common in controller config INIs.

[CookiePLMonster]

Ugh my bad, of course I meant thousands separators.