Variable Substitution: Options for enabling substution in command strings & for applying {fmt}-style number formatting

[florianessl]

This PR enables two new features:

• Variable substitution in interpreter command strings (default CommandCodeInserter is used -> \v, \n, \t)
• Number formatting using {fmt}
  just write the format specification after a ':'
  the parser will ignore anything that is not valid fmt syntax (also decimal types & 'precision' are not supported)

These two features require setting new liblcfs fields which are specified as follows:

System,easyrpg_var_substitution_in_commands,f,Boolean,0xDC,False,0,0,Enables substitution of '\v' '\n' '\a' inside string parameters of interpreter commands
System,easyrpg_var_substitution_formatting,f,Boolean,0xDD,False,0,0,Enables '{fmt}'-style format specifiers for usage inside variable substitution

Example: Graphics customization

Consider you want to dynamically change an actor graphic or faceset depending on some settings.

With this branch you can just use any pre-existing command like this:

com.string: "Actor\v[123:02d]"

... which evaluates to "Actor01.png", "Actor02.png", ..., "Actor[xx].png" depending on the value of Variable '123'

[Ghabry]

Supporting string substitution for the event string arg sounds a bit insane xD. But it could be useful (and faster than always doing a round trip through a String Variable).

I think I cannot accept this without additional unit tests to verify that the fmt-style args work properly.

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Minor: Bit unfortunate that this requires always copying com.string even when the evaluation is disabled. I wonder if this can be prevented 🤔

[florianessl]

Oh, haven't thought about the reference not working there. Stupid me.
I'l look into how I can improve this without any unnecessary copying, and unit-tests for the formatting were definitely on my mind, I'm just working on several branches right now and am constantly shifting my focus :D

I'm working on an extensive test suite for my three main branches, which hopefully will cover all sorts of use cases:
"ScopesVars", "MapInitTrigger" & this one. So, no need to go over any of those while this is still a work-in-progress (also, I'm on holiday for two weeks, so it will take some time.)