Fix var_export/print_r Reflection param names to value (#23308)

[PurHur]

Summary

• Override BuiltinParamNames for var_export / print_r so Reflection reports Zend stub names value,return (InternalArgInfo still says var)
• Named value: / return: calls work; legacy var: is rejected
• php-src ref: ext/standard/basic_functions.stub.php

Lane B note: language/behavioral IR empty; claimed Reflection signature parity with lane-overflow note (STD Lib queue unclaimed).

Closes #23308

Test plan

• ./script/docker-exec.sh -- bash -lc 'php bin/vm.php test/repro/issue_23308_var_export_print_r_reflection.php'
• ./script/phpunit.sh --filter Issue23308VarExportPrintRReflectionTest
• ./script/phpunit.sh --filter VarExportPrintRReflection23308

Verification transcript

$ ./script/docker-exec.sh -- bash -lc 'php bin/vm.php test/repro/issue_23308_var_export_print_r_reflection.php'
var_export:value,return
print_r:value,return
array (
  'a' => 1,
)
Array
(
    [0] => 1
)
Unknown named parameter $var
EXIT:0

$ ./script/phpunit.sh --filter Issue23308VarExportPrintRReflectionTest
OK (2 tests, 6 assertions)

$ ./script/phpunit.sh --filter VarExportPrintRReflection23308
OK (2 tests, 2 assertions)  # VM + JIT

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