Fix manual Throwable getTrace() empty on construct (#9905)

[PurHur]

Summary

• Snapshot caller stack in Throwable::__construct as manualConstructTrace so getTrace() returns array(1) when an exception is constructed inside a user function without being thrown (Zend zend_exceptions.c parity).
• captureOnThrow clears the manual snapshot and still fills trace on throw; rethrow with existing trace unchanged.
• ExceptionGetTrace resolves manual snapshot when trace property is still empty.

Closes #9905

php-src reference

• Zend/zend_exceptions.c — trace capture on manual construct vs throw

PHP implementation

• lib/VM/ExceptionTrace.php — captureOnManualConstruct, resolveTraceVariable
• lib/VM/ExceptionSupport.php — hook construct paths
• lib/VM/Builtin/ExceptionGetTrace.php — resolve snapshot
• lib/VM/ObjectEntry.php — manualConstructTrace field

Verification

./script/docker-exec.sh -- bash -lc '
php test/repro-maintainer/throwable_trace_matrix.php
php bin/vm.php test/repro-maintainer/throwable_trace_matrix.php
php vendor/bin/phpunit test/compliance/VMTest.php --filter "throwable_manual_construct_trace|throwable_get_trace"
'

Output (VM after fix):

Exception::getTrace array(1)
Error::getTrace array(1)
TypeError::getTrace array(1)
OK (2 tests, 2 assertions)

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