[WIP] Fix F# 5.0 regression in overload resolution

[dsyme]

I took a look at https://github.com/dotnet/fsharp/issues/12860 which was a regression in overload resolution in F# 5.0 when some rules around Nullable interop were added mainly for C# optional parameters.

This proposed fix adjusts overload resolution to match F# 4.7 in this case by preferring methods that do not use the F# 5.0 nullable interop conversions.

This will need more work:

• [ ] While this is a bug fix, the adjustment itself might need to be under a language version switch. TBD
• [ ] Testing needs to be added (so far only tested manually on the repro in the bug)

[dsyme]

@NinoFloris Do you know if this is fully covered by #13673?

[NinoFloris]

Yes, modulo the improved representation of the conversion info.

Also https://github.com/dotnet/fsharp/issues/12946 is similarly fixed but still open.

[vzarytovskii]

Since it was fixed, going to close this one, feel free to reopen.