Opt-in (allowlist) mode for `no-unlocalized-strings`

Nobody has claimed this yet.

Currently, `no-unlocalized-strings` operates on an "opt-out" / denylist approach (checking all strings by default unless explicitly ignored). This requires maintaining large lists of `ignoreFunctions` and `ignoreNames`, and it becomes especially cumbersome when working with:

* JSXElements that define string-typed non-rendereable attributes.
* Several functional HTML attributes like `aria-selected`.

For many projects, an opt-in approach, even if less thorough, provides a compromise between correctness and configuration overhead.

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The proposal here is to introduce an opt-in mode for the linter, so rather than `ignore*` lists, the linter supported `check*` lists (or a similar prefix name), where it will only look at attributes, functions, and identifiers that match those lists.

JSX text nodes should still be checked tho

Start by reading the existing no-unlocalized-strings rule and its ignoreFunctions and ignoreNames configuration. Trace how JSX attributes, functions, identifiers, and JSX text nodes are selected, then inspect the rule's tests if available. Done means an opt-in configuration checks only matching items while JSX text nodes remain checked.

Written by the indexing model from the issue text.