Add .findLast() and .findLastIndex()

[m-basov]

microsoft#48829

Describe your changes
Add type definitions for Array.prototype.findLast() and Array.prototype.findLastIndex() methods. Both methods were added to the es2023 target but the target didn't exist so I've created it. The definitions are identical to .find() and .findIndex() but with the updated comments.

Testing performed
Added findLast.ts test file were all Array interfaces try to call .findLast() and .findLastIndex().
Also, tested it manually by running:

• tsc with the es5 target and libs: []
• tsc with the es5 target and libs: ["es2023"]
• tsc with the es5 target and libs: ["esnext"]

Additional context
The es2023 target were added with the help of this PR microsoft#46291

[mkubilayk]

Looks great - one small comment.

[mkubilayk]

Is this test relevant to your changes?

[m-basov]

I believe it was created because the es2023 target was added (filename is callChainWithSuper(target=es2023).js). This file was added for the es2022 target as well.

[acutmore]

I wonder if adding es2023 as a target should be separated out as a separate PR. es2023 doesn't exist yet as a spec so it doesn't feel right that TypeScript would offer it as a target yet. 'esnext' seems more appropriate for now.

[mkubilayk]

Daniel suggests adding them to ES2023 in microsoft#48829 (comment).

[acutmore]

Daniel suggests adding them to ES2023 in microsoft#48829 (comment).

Ah cool. Thanks. I can also see that TypeScript also added es2022 before the spec was official so does seem like there is precedent for this. I'm happy.