Map classes to their valid `FileFormat` enum types

[mferrera]

Validating file types is quite ad-hoc for importing and exporting at the moment. Imports have generally been moved to check again the new FileFormat enum

xtgeo/src/xtgeo/io/_file.py

Lines 48 to 51 in 33652a2

	class FileFormat(Enum):
	RMSWELL = ["rmswell", "rmsw", "w", "bw"]
	ROFF_BINARY = ["roff_binary", "roff", "roff_bin", "roff-bin", "roffbin", "roff.*"]
	ROFF_ASCII = ["roff_ascii", "roff_asc", "roff-asc", "roffasc", "asc"]

but exports have not yet so far, for practical reasons. We should map the class types to the keys of this enum where appropriate to unify file format checking for import and export. This presumes that import file types and export file types are the same, which may not be the case -- in which case they can be grouped into import and export types, respectively.

This mapping might exist inside or outside of the class itself.