support map index match

[peakle]

rule:

	m.Match(`$_{$*_, $_: strings.Compare($s1, $_), $*_}`,
		`$_{$*_, strings.Compare($s1, $_): $_, $*_}`).
		Report(`don't use strings.Compare on hot path, change it to built-in operators`).
		At(m["s1"])

test data:

func f() {
	_ = map[int]int{
		// doesn't match this 
		strings.Compare("", ""): 0,
	}
}

[quasilyte]

It looks like tests are passing:
#361

Is there any extra context that should be taken into account to reproduce this issue?

[peakle]

i tested it on gocritic master on this commit, maybe it related to dependecies version
https://github.com/go-critic/go-critic/tree/319a0d4b91da874eb6f0cdbbf57f8669a0ac13c6