Preserve get_called_class in directly compiled methods

[yavon007]

A final instance method on a concrete class can be called directly by generated
C++ code. If it calls get_called_class(), the generated runtime function call
has no Zend method frame to inspect and raises “must be called from within a
class”, even though the same PHP program correctly returns the runtime class.

For zero-argument named calls resolved to this built-in in ordinary compiled
methods, reuse the receiver/called-scope machinery used by static::class.
Apply this after user-function resolution and argument validation. Use the
parser-resolved function target to distinguish case-insensitive aliases. Leave
dynamic calls, first-class callables, Native-class restrictions, and calls
outside methods on their existing paths. Do not expand devirtualization.

Validation: 149 focused PHPUnit tests / 302 assertions pass. A new compiled
PHPT matches PHP and EXPECT for inherited instance/static calls, traits,
mixed-case fully qualified names, aliases, closures, runtime subclasses,
namespaced function shadowing, and the error outside class scope. The minimal
unmodified-compiler repro exits 255; the fixed build matches PHP with empty
stderr. Tested on Linux ARM64, GCC O2, PHP 8.5.10 ZTS and PHPX 4b3a472.

This is a correctness fix with no claimed benchmark gain; it is not a general
solution for every runtime API that inspects Zend execution frames.