[built-in-ai] Implement AITranslatorCapabilities

This CL implements AITranslatorCapabilities with `available` attribute
and `languagePairAvailable()` method.

AITranslatorCapabilities.languagePairAvailable() method is a synchronous
method which returns the capabilities of a language pair. But
unfortunately, the logic of calculating the capabilities of each
language pair is very complicated because of the
TranslationAPIAcceptLanguagesCheck and
TranslationAPILimitLanguagePackCount features which were introduced
for protecting the user's privacy during the Origin Trial experiment.

It is possible to calculate the capabilities of each language pair
synchronously in Blink, if we send the state of these two features, the
user's accept languages, the list of supported language packs and the
list of installed language packs to Blink, and implement the
calculation logic in Blink duplicating the logic in the browser
process. But this makes the mojo IPC and Blink code too specialized to
Chrome's translation library. This makes it hard for other embedder to
implement the Translation API. So we decided to implement a more generic
solution.

The solution is to introduce language categories and an availability
matrix. The all supported languages are divided into several categories
based on the user's accept languages and the installed language packs,
and whether the language is popular or not. And then we create an
availability matrix which represents the capabilities of each language
pair based on the language categories.

The availability matrix is a 2D array of TranslationAvailability which
represents the capabilities of each language pair based on the language
categories.

The browser process sends the language categories and the availability
matrix to Blink. So the languagePairAvailable() method in Blink only
needs to return the corresponding element in the availability matrix
according to the given source and target language categories.


Note: This CL was originally created by yuzus@. horo@ took over this
work. This CL's PS1 is the clone of the original CL
https://crrev.com/c/5963884/32 .

Bug: 378992891
Change-Id: I50e7434b6cfac4da4cc0040d81188ebf98f01ce3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6038986
Reviewed-by: Takashi Toyoshima <toyoshim@chromium.org>
Reviewed-by: Fergal Daly <fergal@chromium.org>
Commit-Queue: Tsuyoshi Horo <horo@chromium.org>
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Reviewed-by: Igor <igorcov@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1391552}