fixes failures on expression-bodied constructors

[ophura]

these changes enable support for expression-bodied constructors, such as:

public class UserDefinedClass
{
    private readonly int _value;

    // NOTE: this now compiles
    public CustomUserClass(int value) => _value = value;
}

the above code as is fails in the current implementation, the proposed modification fixes the failure.

additionally, I further proposed other changes regarding the internal UdonSharpInternalUtility.GetTypeID utilitarian subroutine, those changes preserve the previous behaviour of the subroutine; therefore the changes are benign. it is mainly for modernization reasons (although it is slightly more performant).

is SHA256 really needed for the purpose of hashing? if not, will it be a breaking change to use a much more efficient algorithm?
I had XxHash64.HashToUInt64 (from System.IO.Hashing) in mind as a much, much faster and memory efficient alternative; if there isn't much interest in improving performance, then don't mind my suggestion.

[Deantwo]

Looks fine to me.

Not sure why you changed // to /* */ though.

[ophura]

@Deantwo I don't exactly remember... I think I tried to uncomment it to see what the IDE (VS) had to suggest, and then reapplied the comment using CTRL + SHIFT + / once I was done with it. the /* ... */ comment style was the one pick by the IDE... yeah, that's probably what happened. I can revert it to the more idiomatic commenting style if it's necessary.