[Property Editor] Check for registered LSP service methods before calling them

[elliette]

Fixes #8715
Work towards #1948

• Waits for the editArgument and editableArguments service methods to be registered on the LSP service before loading the property editor.
• Uses either the experimental or non-experimental method depending on which one is registered.

[kenzieschmoll]

nit: a switch statement may be easier to read than this long chain of if / elses

[elliette]

It would be but unfortunately these are all getters, triggering the error: "Extension methods can't be used in constant expressions." (I'm guessing that is why this was written as a bunch of if statements in the first place)

[DanTup]

Uses either the experimental or non-experimental method depending on which one is registered.

It's not a big deal, but I think it may have been better to hold off on this - the reason for the prefix was in case we needed to make any breaking changes, we could be sure there wasn't a version of PE/Server out there that try to communicate with different versions of the protocol (unless they were experimental versions).

(I think the API is fairly stable and changes will probably be compatible, although I'm not certain how we'll handle removing arguments yet)

[elliette]

Uses either the experimental or non-experimental method depending on which one is registered.

It's not a big deal, but I think it may have been better to hold off on this - the reason for the prefix was in case we needed to make any breaking changes, we could be sure there wasn't a version of PE/Server out there that try to communicate with different versions of the protocol (unless they were experimental versions).

Ah got it! I think we can remove the non-experimental endpoints for now, and then add them back in when ready. I'll send out a change.