ext/reflection: Make properties readonly

[kamil-tekiela]

Fixes #24147 alternative to #24153

It should not break BetterReflection.

[kamil-tekiela]

@ndossche According to the test, this should still allow unset, even though I think it would be better not too. The BC changes are minimal here: the properties cannot be redeclared. As such, I think it may even go on PHP 8.4.

@Ocramius What is your opinion on this?

[Ocramius]

even though I think it would be better not too

An alternative could be to interface the properties, FWIW - requires some more substantial changes.

unset() is the only mechanism I currently know of to allow shadowing a property with additional logic: if property accessors allow overriding a parent property, that's also a viable idea.

[Ocramius]

BTW, if you want, just take the phpunit suite of BetterReflection for a spin on this branch: it is very detailed