Replace the global state variables and functions of potx with services

Problem/Motivation

potx holds its extraction state in 16 global arrays, shared by about 70 global functions in potx.inc and its include files. Every caller resets that state by hand: the tests reset $_potx_store, $_potx_strings and $_potx_install, and l10n_server unsets every $_potx_* global around each release it parses. Schema storage is configured through function names in $_potx_callbacks, reporting through a static mode of potx_status(), and the extract form prints the download and ends with exit.

Proposed resolution

• A Potx service starts an ExtractionRun, which owns the state of one extraction: strings, diagnostics, config schema and YAML translation patterns. No global state is left behind.
• One internal extractor service per file type: PHP, JavaScript, Twig, YAML and .info. PHP extraction uses token_get_all(), with a token stream per file and one recognizer class per construct. Twig templates are lexed with potx's own environment, independent of the site's extensions.
• An ApiVersion enum with Drupal5, Drupal6, Drupal7 and Modern (Drupal 8 and later) selects the recognizers.
• Config schema and shipped configuration get their own classes; the six schema callbacks become a SchemaStorageInterface that l10n_server can implement.
• Value objects for strings, occurrences and diagnostics; callers present the diagnostics (Messenger, Drush, arrays).
• A template builder and writer produce one template. The form returns a streamed download, and services are injected into the form and the Drush command (Drush 13 or later).
• Removed as outdated: the CVS $Id$ versions (the header should list the paths of the source files only), the multiple and core builds, installer strings as a separate kind, and the fallback t().
• potx.inc becomes a compatibility layer over the services, deprecated for removal in 3.0.0.

Remaining tasks

Do it. First Remove the outdated output; in testDrupal5() to testDrupal7(), installer strings become ordinary strings. After that generated test templates should be byte-identical at every step.

LLM disclosure

LLM was used to create the high level plan and do implementation for this issue. With human review. Attached full plan.