Resolve function imports before dispatch and policy checks

[yavon007]

Calls through use function aliases can resolve to the wrong target when the
call's casing differs from the import, or when a same-named compiled global
function exists. For example, a user function imported as GET_CALLED_CLASS
is bypassed by get_called_class(), causing the built-in to run and throw.

Normalize function-alias keys during registration and lookup. When an
unqualified call names an imported function, use only the imported target for
native-function resolution rather than checking global functions first.
Keep absolute/qualified calls and class/constant imports unchanged.
Resolve the imported target before special-function and capability-policy
checks as well: safe functions must not be rejected because their alias names
a restricted built-in, and restricted functions must not evade policy through
an innocuous alias.

Add codegen and PHP/AOT behavioral coverage for mixed-case aliases, built-in
aliases, grouped imports, global name collisions, and explicit global calls.
Codegen assertions verify the selected imported and global targets; the
compiled regression matches PHP output exactly with empty stderr.
Additional compile-only tests ensure an imported exec alias is rejected under
both Nano and WASI, while a user function aliased as extract remains callable.

Focused PHPUnit: 115 tests / 632 assertions pass (11 existing deprecations).
The complete 135-file compiler self-build and --version check pass. The
resulting compiler also builds and runs the regression with PHP-identical output.
Tested on Linux ARM64, PHP 8.5.10 ZTS, GCC and PHPX 4b3a472. No benchmark
speedup is claimed.