Modernize Docker test images & fix PHP 8.3 / 8.5

[endelwar]

The docker/Dockerfile{83,84,85} images used by make tests were built with the
now-deprecated pecl install, shipped the developer's local vendor/ into the
image, and forced an incompatible Symfony version on PHP 8.3.

Changes

• pecl → docker-php-extension-installer for the mongodb extension and Composer. pecl is officially deprecated by the MongoDB PHP driver. Build deps are now auto-removed.
• Unify mongodb on 2.3.3 across all three images (was 1.17.0 / 1.21.0 / 2.1.2).
• Pin 8.5 to stable php:8.5-alpine (was 8.5.0rc3-alpine which is unavailable) — the suite now runs on PHP 8.5.
• Drop --ignore-platform-reqs: on the PHP 8.3 image it let Composer install Symfony 8.x (which requires php >=8.4.1) instead of the highest compatible release, so the whole suite failed to load with a ParseError on Symfony's property-hook syntax. Without the flag, PHP 8.3 resolves Symfony 7.4 and the suite passes. composer check-platform-reqs is green on all three images, so the flag was only bypassing the PHP version constraint — no required extension is missing.
• Add .dockerignore so a vendor/ built on the developer's machine is no longer copied into the Linux image.
• BuildKit cache mount for Composer's download cache (replaces composer clear-cache): fast rebuilds without freezing dependency resolution.

Results

Metric	PHP 8.3	PHP 8.4	PHP 8.5
Image size before	498 MB	503 MB	529 MB
Image size after	190 MB	194 MB	221 MB
Reduction	−62%	−61%	−58%
Tests	✅ 356	✅ 356	✅ 356 (was broken)

Build metric	Before	After
Build context transferred	~50 MB	17.8 kB
Composer re-download on rebuild	full	0 (cache mount)
Composer step (warm cache)	5.0 s	2.4 s

All 356 tests pass on PHP 8.3, 8.4 and 8.5.

[endelwar]

PHP-CS-Fixer issues not related to PR

[garak]

@endelwar I just tried to run TARGET=84 make tests on branch 3.x and got the following problem (omitting the previous steps for brevity):

Step 7/8 : RUN --mount=type=cache,target=/tmp/composer-cache COMPOSER_CACHE_DIR=/tmp/composer-cache composer update --prefer-dist
the --mount option requires BuildKit. Refer to https://docs.docker.com/go/buildkit/ to learn how to build images with BuildKit enabled
make[1]: *** [Makefile:29: vichuploader-image] Errore 1
make[1]: uscita dalla directory «/foo/VichUploaderBundle»
make: *** [Makefile:7: tests] Errore 2

[endelwar]

BuildKit is standard from Docker Engine 23 released in february 2023, which versione are your running?

[garak]

$ docker --version
Docker version 29.1.3, build 29.1.3-0ubuntu4.1

Edit: solved with a sudo apt install docker-buildx