Add support for :extend-via-metadata in protocol definitions

[vlaaad]

With release of 1.10.0-beta6 behavior for metadata-based protocol extension is now opt-in and requires to supply option to enable it:

(defprotocol Component
  :extend-via-metadata true
  (instance [this] "returns platform instance associated with this component"))

After adding :extend-via-metadata true Cursive can't see method declarations:

I hope Cursive will get support for this one day!

[vlaaad]

You are awesome, Colin, thank you!

[sooheon]

Not sure if there has been a regression, but with v1.8.2-eap4-2019.1, I still see this issue:

[jffry]

@sooheon If you're still having this issue, I narrowed down the cause. Try moving :extend-via-metadata true after the docstring for the defprotocol and Cursive should understand it. I opened a related issue for this: #2429