Removing @rust-nofix from match_same_arms requires lint fixes

[scottgerring]

Summary

In #13803 together with @blyxyas we discovered that match_same_arms does not deal with cases where more than 2 arms have the same body. E.g. this test:

rust-clippy/tests/ui/match_same_arms.rs

Lines 31 to 38 in 6a3ef93

	let _ = match 42 {
	1 => 2,
	2 => 2, //~ ERROR: this match arm has an identical body to another arm
	//~^ ERROR: this match arm has an identical body to another arm
	3 => 2, //~ ERROR: this match arm has an identical body to another arm
	4 => 3,
	_ => 0,
	};

Will generate two overlapping suggestions - one to combine 1 and 2, one to combine 2 and 3. This means the lint cannot be automatically applied, and @rust-nofix remains.

It looks like the issue is that the arms are matched up pairwise, rather than collecting all that have the same body and suggesting an aggregate fix:

rust-clippy/clippy_lints/src/matches/match_same_arms.rs

Lines 115 to 116 in 6a3ef93

	for (&(i, arm1), &(j, arm2)) in search_same(&indexed_arms, hash, eq) {
	if matches!(arm2.pat.kind, PatKind::Wild) {

We should change this to aggregate all equivalent bodies and provide a single suggestion to combine them.

Reproducer

Remove @rust-nofix from match_same_arms and check out the overlapping application failure for the test code linked above.

Version

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