[12.x] add a $ when referencing a class property

[browner12]

consistently prefix with a $ when referencing a class property.

this is a follow up to #10645

I explicitly only added the prefix when we were directly referencing and showing an example of a PHP class. I did not add the prefix when referencing a javascript property of an object, or when the example showed the calling code of the property from an instantiated object ($model->property).

if I'm being honest, I think the previous PR went the wrong direction, and instead we should remove all the $ prefixes. it feels like the $ is implied for all PHP class properties. we also get this inconsistency, because it becomes largely context dependent on what type of property we're referencing, and how we're showing it in the example. but I'll obviously leave that up to maintainers to decide on.

[AhmedAlaa4611]

it becomes largely context dependent on what type of property we're referencing, and how we're showing it in the example.

According to your description, I think we may need to remove the prefix.

[browner12]

correct. Taylor can decide if he wants to accept this PR, which matches your changes from the previous PR. or if he'd like to revert and go the other direction.

[taylorotwell]

Just reverted the other PR.