Extend use-in-operator to contains check in partial rule sets (or set values)

[anderseknert]

This rule currently flags locations where "foo" := bar[_] can be replaced with "foo" in bar. We should extend this to cover also the case of foo["bar"], when foo is known to be a partial rule or a set value, as using in is reasonably considered more idiomatic there too.

Avoid

package p

import rego.v1

partial contains "foo"

allow if {
    partial["foo"]
    # or
    partial.foo
}

Prefer

package p

import rego.v1

partial contains "foo"

allow if {
    "foo" in partial
}