Return snake-cased member name from str() on enum values

[jhonabreul]

Description

C# enum members are exposed to Python with upper-cased snake case names (e.g. FileAccess.READ_WRITE), but converting an enum value to a string returned the C# member name from Enum.ToString() (e.g. "ReadWrite"), so the string representation did not round-trip with how the member is accessed from Python.

EnumObject now overrides the tp_str slot so that str() (and f-string formatting) return the same Python-facing snake-cased name used to access the member:

str(DayOfWeek.SATURDAY)                  # "SATURDAY" (was "Saturday")
str(FileShare.READ_WRITE)                # "READ_WRITE" (was "ReadWrite")
str(FileShare.READ | FileShare.DELETE)   # "READ, DELETE" (was "Read, Delete")
str(Enum.ToObject(DayOfWeek, 10))        # "10" (unchanged: no defined member)

String equality comparison also accepts the snake-cased name now, consistently with str(), while still matching the C# member name:

FileShare.READ == "Read"   # True (unchanged)
FileShare.READ == "READ"   # True (was False)

Note this is a behavior change for code that logs, serializes or compares str(enum_value) expecting the C# member name.

Includes the version bump to 2.0.61.