Mark writes that are really reads if working on an object

[nikic]

Alternative to #5250 that I think handles the readonly property case more comprehensively.

We add a flag to the FETCH_OBJ_W/RW/UNSET opcodes that tells us whether the write should be interpreted as a read if the fetched value is an object. This is passed on to read_property as an extra flag in the BP_VAR mode.

Here this is used to make the "indirect modification" warning more accurate -- but the same check would also apply to readonly properties.

This change is likely incomplete because it makes BP_VAR a mask, so some equality comparisons may need to be adjusted.

[nikic]

As readonly properties were declined, and this implementation does not require BC breaks, I'm closing this for now...