THRIFT-6167: Fix PHP HTTP response framing in cross-tests

[sveneld]

Fixes the remaining php->cpp HTTP cross-test failures on current master after THRIFT-6023 and THRIFT-6060 landed.

Changes:

• add Content-Length to synchronous responses from test/php/HttpServer.php so the C++ HTTP client can consume PHP HTTP replies correctly
• preserve the PHP launcher flags when test/php/HttpRouter.php execs into php -S
• remove the now-passing php-cpp_{binary,compact,json}_http-ip cases from test/known_failures_Linux.json

Validation:

• php->cpp HTTP: binary, compact, json
• cpp->php HTTP: binary, compact, json, multi-binary, multic-compact, multij-json

JIRA: THRIFT-6167
Generated-by: OpenAI Codex GPT-5

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