feat: Support extract variable in macro call

[A4-Tacks]

Implement based first and last token mappings

Example

macro_rules! foo {
    (= $($t:tt)*) => { $($t)* };
}

fn main() {
    let x = foo!(= $02 + 3$0 + 4);
}

Before this PR

Assist not applicable

After this PR

macro_rules! foo {
    (= $($t:tt)*) => { $($t)* };
}

fn main() {
    let $0var_name = 2+3;
    let x = foo!(= var_name + 4);
}

[ChayimFriedman2]

Nice, this is useful!

Can you please add a test where the block we extract into is inside the macro call?

View changes since this review

[rustbot]

This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[A4-Tacks]

At present, it only supports extraction into outside of macros, and there may be improvements in the future

[ChayimFriedman2]

Then test that it's not applicable in a macro?

[A4-Tacks]

At least for small macro calls, extracting to outside the macro is very practical

Supporting extraction to inside the macros may disrupt mappings
If this is check and not applicable, it is easy to false negative

[ChayimFriedman2]

I'm just saying that whatever the current behavior is, it's good to test it, so we won't have surprises now or in the future.

[A4-Tacks]

it's good to test it

Oh, I have already pushed the test