fix: Fix ref_match position when keyword prefix

[A4-Tacks]

This is a quick fix, please review if there is a regression

Fixes #15139
Fixes #18572

Example

fn foo(data: &i32) {}
fn main() {
    let indent = 2i32;
    foo(in$0)
}

Before this PR

fn foo(data: &i32) {}
fn main() {
    let indent = 2i32;
    foo(in&dent)
}

source_range: 65..67,
delete: 65..67,
ref_match: "&@67",
..

After this PR

fn foo(data: &i32) {}
fn main() {
    let indent = 2i32;
    foo(&indent)
}

source_range: 65..67,
delete: 65..67,
ref_match: "&@65",
..

[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.