fix(lsp): pass server resp through client handlers (1)

[jamestrew]

For LSP methods/pickers:

• references
• definition
• typeDefinition
• implementation

Passes the server results through client (and neovim's) lsp handler function.
This lets those handlers deal with some of the language server specific idiosyncrasies.

Also refactors shared code between these pickers.

Other pickers/methods will need similar treatment.

[solson]

Thanks for the quick PR! When I re-try my reproduction steps from #2768, I run into this error:

Error executing vim.schedule lua callback: ...ker/start/telescope.nvim/lua/telescope/builtin/__lsp.lua:147: attempt to index local 'location' (a nil value)
stack traceback:
        ...ker/start/telescope.nvim/lua/telescope/builtin/__lsp.lua:147: in function 'handler'
        ...eovim-unwrapped-0.9.4/share/nvim/runtime/lua/vim/lsp.lua:1393: in function ''
        vim/_editor.lua: in function <vim/_editor.lua:0>

Which suggests that local location = items[1].user_data was nil.

[jamestrew]

Ah.. it's probably a neovim version issue.
It looks like I'm relying on some bleeding edge changes on nightly (neovim/neovim#25830)

I think we're planning to bump the minimum neovim version requirement to 0.10 for telescope v0.2.0 but there's no timeline for that. Either we come up with a different approach or can't merge this until then.

I'm not sure if I'm in love with my solution anyways. This relies on the custom handlers eventually calling neovim's builtin handler or supporting a on_list option like the builtin one does. And I don't think this is a requirement for lsp handlers.