Web: populate $_SERVER HTTP_* from request headers (#193)

[PurHur]

Summary

• Map incoming HTTP request headers to CGI-style $_SERVER['HTTP_*'] keys in DevServer for both VM bin/serve.php and AOT serve-aot CGI env (closes Web: Populate $_SERVER['HTTP_*'] and REQUEST_URI from incoming headers #193).
• Clear stale HTTP_* keys between requests on the long-running dev server.
• Reject header values containing CR/LF; cap header count and value length (partial Security: Request body size limits and header sanitization in CGI driver #77).
• Add PHPT web_http_headers.phpt, unit tests, and a ServeTest integration case.
• Add Ubuntu 22.04 + PHP 8.2 dev Docker image (make docker-build-22, make test-docker, script/docker-ci-local.sh) and README container docs (progress on Infrastructure: Publish Docker dev image and document container CI workflow #202, Infrastructure: Upgrade Docker images to Ubuntu 22.04 + PHP 8.2 toolchain #73).

Test plan

• php vendor/bin/phpunit test/unit/Web/DevServerHeadersTest.php
• php vendor/bin/phpunit test/real/cases/web_http_headers.phpt
• Web PHPT cases in php-compiler:22.04-dev Docker image
• ServeTest::testPopulatesHttpServerHeaders on hosts that allow TCP bind in Docker

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