Eliminate needless returns

[compiler-errors]

This is Rust, not Java! Returns are not necessary unless they interrupt control flow!

Fixes instances of clippy::needless_return. This is especially jarring when it's paired with match branches that do not return, like:

if whatever {
    return Some(x);
} else {
    None
}

or

match whatever {
    Variant => true,
    OtherVariant => return false,
}

... since it suggests that some exceptional control flow is happening even though it isn't.

I also tried to turn some:

if whatever {
    side_effect();
    return true;
}
return false;

into:

if whatever {
    side_effect();
    true
} else {
    false
}

Though I only did it when I noticed it.

[rustbot]

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[rustbot]

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

Some changes occurred to the CTFE / Miri engine

cc @rust-lang/miri

Some changes occurred to the CTFE / Miri engine

cc @rust-lang/miri

[RalfJung]

Duplicate of #130114?

[compiler-errors]

Yep! Glad that's getting fixed lol