Allowing Usage of `CHR$` in `CONST` Statements

[a740g]

Currently, QB64-PE supports the usage of _RGB32 and _RGBA32 in CONST statements, which allows for improved code readability and maintainability when working with color values. It would be beneficial to extend this capability to include the CHR$ function within CONST statements as well.

This would enable folks to define constants representing ASCII characters or sequences, like how _RGB32 constants are currently supported when working with color values. The proposed behavior would allow code like the following to be valid:

CONST CRLF = CHR$(13) + CHR$(10)