Support &=, ^=, |= for macros

[davispuh]

Consider macro like this:

#define FLAG_CLEAR(S, Flag) (S->Flags &= ~(Flag))

Currently such macros with &=, ^= and |= are dropped.
So this PR implements support for them and will produce D code like:

extern (D) auto FLAG_CLEAR(T0, T1)(auto ref T0 S, auto ref T1 Flag)
{
    return S.Flags &= ~Flag;
}

[Copilot]

Pull request overview

This PR updates the macro expression parser so macros using compound bitwise-assignment operators (&=, ^=, |=) are no longer dropped and can be translated into equivalent D expressions.

Changes:

• Added parsing support for &=, ^=, and |= in macro expressions.
• Routed conditional-expression parsing through the new compound-assignment parse layer.

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[jacob-carlborg]

There's no test added.

[davispuh]

I fixed operator precedence and added tests.