No longer store MethodData as static variables

[metoule]

#349 (via commit 0346c9d) removed the reflection code that was used to know the operands of binary and unary operators. Instead, it stored MethodData object as static objects, so that they could directly be used during the resolution process.

That proved to be an ill-advised choice: the resolution process mutates the MethodData class, but since they're stored as static variables, it was not thread-safe: thanks @mats-boisen for the investigation in #364!

This PR instead stores immutable objects as static variables. The MethodData used during resolution is therefore created for each resolution.

Fix #361
Fix #364

[holdenmai]

@metoule What are your thoughts on having the static fields and updated method signatures be Method base instead of the SimpleMethodSignature? Obviously the actual ones you return would still be the simple class.

This may allow us to transform some things going forward if we make further changes/optimizations around how these operations are looked up.

[davideicardi]

Thanks!

[davideicardi]

@metoule Thank you!

Just a question to fully understand:
When the MethodData will be created exactly with this new PR?

[metoule]

When the MethodData will be created exactly with this new PR?

In Parser.PrepareOperandArguments, when we call MethodResolution.FindBestMethod(signatures, args): that overload converts the MethodBase to MethodData.