Resolve cObject variables in per-file includeCSS blocks (v13 backport)

[svewap]

Backport of the first half of #105 to release/v13. The v13 branch has the same bug: only the global plugin.tx_wsscss.variables path resolved content objects, while the per-file page.includeCSS.<key>.variables block took the TypoScript array verbatim (array_filter($subConf['variables.'] ?? []), line 140).

A cObject variable (myVar = TEXT + myVar.value = …) therefore kept its myVar. sub-array, which reached Compiler::compileFile() and hit implode(',', $variables):

PHP Warning: Array to string conversion in …/ws-scss/Classes/Compiler.php line 82

TYPO3's error handler turns that into an exception → HTTP 500 in the frontend. It is easy to hit, because copying the global block per file is the documented way to scope variables to a single file, and t3bootstrap does exactly that.

Both paths now share parseTypoScriptVariables().

Not backported: the setRequest() part of #105. ContentObjectRenderer::getRequest() still has an undeprecated $GLOBALS['TYPO3_REQUEST'] fallback in v13 (only a @todo in core), so that change has no effect here and is left out to keep the diff minimal.

Verification

TYPO3 13.4.29-dev, PHP 8.4.20, scssphp 2.1.0. Driving renderPreProcessorProc() with a per-file block containing cobj-test = TEXT / .value = 3px, a nested COA (10 = TEXT/10.value = 7, 20 = TEXT/20.value = px) and a plain 11px:

before

THROWN: TYPO3\CMS\Core\Error\Exception
  PHP Warning: Array to string conversion in …/ws-scss/Classes/Compiler.php line 82

after

.probe {
  padding: 3px;
  margin: 7px;
  gap: 11px;
}

No regression on the setups that already worked — global block, per-file plain values, and global cObject all compile to byte-identical CSS with and without the patch (md5=9222d0fbf812c3ec0f495bea1360b9db in all six runs).