Add has-property- assertion

[weirdan]

On itself it doesn't do much good as property fetch analyzer doesn't
support object intersections yet. But it's a groundwork for future
enhancements.

[orklah]

Seems good. Calling isset on a property should probably create that assertion too (though it can't be reverted because the property could just be null or un-initialized)

[orklah]

Does this fix #2206 and maybe #4182?

[weirdan]

though it can't be reverted

By the way, how do we make assertions that can't be inverted?

[weirdan]

Does this fix #2206 and maybe #4182

Not entirely. To fix those, we also need to fix property fetch analysis on intersections.

[orklah]

By the way, how do we make assertions that can't be inverted?

In theory, it's mainly this: https://psalm.dev/docs/annotating_code/assertion_syntax/#equality-assertions

IsIdentical and IsLooselyEqual can't be meaningfully inverted whereas IsType can

But those only work with a specific type that must be given to the assertion. However, I found that we already have an isset assertion (but it doesn't seem to do much with properties). In fact, we have two: IsIsset and IsEqualIsset. The former can be inverted into IsNotIsset but the latter can't (trying to invert it will result in the "useless" assertion:

psalm/src/Psalm/Storage/Assertion/IsEqualIsset.php

Line 14 in f11ed46

return new Any();

)