Description:
------------
On both Twig and Symfony, we noticed that in some performance-critical code paths, the most significant change we could do to improve performance was replacing class constants by their values.

See:
- https://github.com/twigphp/Twig/pull/2636/files
- https://github.com/symfony/symfony/pull/26161/files

While I understand that the reason for this is that opcode arrays are per-file, this could be optimized at runtime, by repalcing the const-fetch by its value on first access (similarly to what is done for non-namespaced functions.)

Test script:
---------------
function foo($a = SomeClassInAnotherFile::FOO)
{
}

function bar($a = 123)
{
}

Expected result:
----------------
Calling foo() and bar() without any arguments should be as fast for both functions.

Actual result:
--------------
Calling foo() is measurably slower than calling bar()