Also check `match`es for `branches_sharing_code`

Description

Example (albeit contrived):

fn main() {
    let s = "RustAnalyzer";
    let mut s2 = String::new();
    for (i, c) in s.chars().enumerate() {
        let mut c2 = c;
        match c {
            'A'..='Z' => {
                if i != 0 {
                    s2.push('-');
                }
                c2 = c.to_ascii_lowercase();
                s2.push(c2);
            }
            _ => {
                s2.push(c2);
            }
        }
    }
    println!("{s2}");
}

Could be written as:

fn main() {
    let s = "RustAnalyzer";
    let mut s2 = String::new();
    for (i, c) in s.chars().enumerate() {
        let mut c2 = c;
        match c {
            'A'..='Z' => {
                if i != 0 {
                    s2.push('-');
                }
                c2 = c.to_ascii_lowercase();
            }
            _ => {}
        }
        s2.push(c2);
    }
    println!("{s2}");
}

(which in this case could get further reduced by single_match)

Version

rustc 1.87.0-nightly (f280acf4c 2025-02-19)
binary: rustc
commit-hash: f280acf4c743806abbbbcfe65050ac52ec4bdec0
commit-date: 2025-02-19
host: x86_64-pc-windows-msvc
release: 1.87.0-nightly
LLVM version: 20.1.0

Additional Labels

No response

Start by locating the implementation and tests for the branches_sharing_code lint in rust-clippy. Compare its current handling of conditional branches with the match example, then add coverage showing the intended diagnostic behavior and run the relevant lint tests to verify it.