Fix GH-10497: Allow const obj->prop = value

[khaledalam]

Description

Fixes #10497 - Allows direct modification of object properties stored in constants.

Problem

Previously, this code would fail with a fatal error:

const a = new stdClass;
a->b = 42;  // Fatal error: Cannot use temporary expression in write context

Solution

Modified the compiler to properly handle ZEND_AST_CONST in variable compilation contexts:

Constants now emit IS_VAR instead of IS_TMP_VAR when used in write contexts
This allows property assignment opcodes to work correctly with constant objects

Tests:

• Added Zend/tests/gh10497.phpt - comprehensive test for the fix
• Updated Zend/tests/gh12102_3.phpt - reflects improved constant handling

Behavior

Now supports all property operations on constant objects:

const obj = new stdClass;
obj->prop = 'value';
obj->prop = 'new value';
obj->another = 'test';
obj->counter = 0;
obj->counter++;
obj->num = 10;
obj->num += 5;
unset(obj->prop);
obj->nested = new stdClass;
obj->nested->value = 123;

The constant reference remains immutable, but the object itself is mutable as expected.