prefer-at: Support private field

[regseb]

Fix #1928

I added case 'PrivateIdentifier': in isSameReference() (cf. #1928 (comment)) but the private fields are still not supported.

prefer-at.mjs › Invalid #20
        1 | class Foo {#bar; baz() {return this.#bar[this.#bar.length - 1]}}

  Invalid case should have at least one error.

  Value is deeply equal:

  []

  › file://test/utils/snapshot-rule-tester.mjs:188:8

  ─

  1 test failed

[fisker]

MemberExpression need update too.

[regseb]

Tests passed with "PrivateIdentifier" in getStaticPropertyName(). 2a9e359#diff

There isn't "PrivateIdentifier" in ESLint. There is a bug in ESLlint? (I don't find a testcase)

[fisker]

I mean this part https://github.com/eslint/eslint/blob/94ba68d76a6940f68ff82eea7332c6505f93df76/lib/rules/utils/ast-utils.js#L420-L443, your solution isn't correct, it will cause this.#foo[this.foo.length - 1] pass.

[regseb]

With my last commit e95cec1, the tests on the private fields are successful.

But 4 tests fail because messages are reported for valid codes:

#	Source	Message
1	a[x].push(1); a[x].push(2);	no-array-push-push: Do not call Array#push() multiple times.
2	foo[bar++].slice(foo[bar++].length - 1)	prefer-negative-index: Prefer negative index over length minus index for slice.
3	foo[a + b].slice(foo[a + b].length - 1)	prefer-negative-index: Prefer negative index over length minus index for slice.
4	foo[`${bar}`].slice(foo[`${bar}`].length - 1)	prefer-negative-index: Prefer negative index over length minus index for slice._

I don't know how to correct this problem. 😞

---

I tested with the no-self-assign rule of ESLint (which uses the isSameReference function). Only case 1 has a problem.

ESLint Playground:

/* eslint no-self-assign: "error" */

let foo = ["a", "b", "c"];
let bar = 0;
let baz = 0;
/* 1 */ foo[bar] = foo[bar];
/* 2 */ foo[bar++] = foo[bar++];
/* 3 */ foo[bar + baz] = foo[bar + baz];
/* 4 */ foo[`${bar}`] = foo[`${bar}`];

6:20 'foo[bar]' is assigned to itself. (no-self-assign)