Handle jdt:// attachments on multiple clients

[fengwk]

I often need to switch between multiple workspaces, so multiple clients are generated.

I need a way to select the client that matches the expected behavior for attach, most of the cases I encounter jump to the buffer pointed to by the jdt protocol, so maybe acquiring the previous buffer’s client for attach might better match expectations.

It’s working fine, at least for now.

[fengwk]

To add the reason for this change:

Before the modification, the contents of the jdt buffer using the wrong client will be decompiled instead of opening the source code.

[mfussenegger]

Makes sense to me. I made a couple of changes (and hope I didn't break it with them) and merged it.

[fengwk]

Great, it's working fine now