Adds a warning when assigning a value in a conditional

[Zonespace27]

When assigning a value in an if() or switch() statement, the compiler will emit an AssignmentInConditional warning.

Closes #576

[ike709]

Wixoa may disagree but I think this should go with the 2000s warning codes since this emission can point out actual logic errors and isn't purely a stylistic choice.

[wixoaGit]

Wixoa may disagree but I think this should go with the 2000s warning codes since this emission can point out actual logic errors and isn't purely a stylistic choice.

So is SuspiciousSwitchCase but that's also a 3000.

Though I am struggling to come up with a distinction between these two ranges. The 2000s are "for compiler configuration of actual behaviour" but this behavior seems to just be error/not error? Not much different from any of the other configurable warning codes.