Multi LSP Server support

[yyoncho]

Fixes #225 #424 #376 #360 #280 #285 #264 #229 #117 #111 #335 #392 #390 #359 #340 #225

Higher level goals:

• Allow multiple servers to work in one project and in one file
• Make finding of project roots easier and more explicit for the users.
• Removed all synchronous calls from the server startup.
• Improved hadling of status messages.
• Implemented workspace folders support as a first class citisen instead of
  being a patch in the existing configuration.
• Simplified the code as much as possible

The following things are implemented:

1. Moved lsp-mode related code into single file. Now clients should either
   require lsp-mode or lsp. After this CL lsp-mode.el and lsp.el extesions
   like ccls and lsp-ui will be able to work against either of these.
   lsp-mode will be used by default and if you want to use the new lsp.el you
   should do (require 'lsp) before loading lsp-mode.

2. Introduced lsp-session which will be resposible for handling project
   session configuration like:

• What currently imported projects.
• What server are running and the folders that are associated with the session.
• What folders are ignored and wont be used to initialize a project in it. The
  session is persisted and automatically loaded the first time user calls lsp

3. Introduced lsp-language-id-configuration which will hold the configuration
   "language" -> emacs major mode. This map is used to render eldoc information and
   also to determine the language id when sending various notifications to the
   server.

4. Restructored lsp--client by removing the runtime related
   stuff (like last-id) so it can be used as a template for registration. This will
   simplify the way lsp client registration and it will make easier to add new
   functionality

5. lsp-ui and company-lsp should be adapted as well. I will prepare separate CLs.

6. Implemented frontend for reviewing what servers are running, which buffers
   are managed, and so on the method have replaced the existing lsp-capabilities
   method.

7. Reworked the modeline so it can provide info for the servers currently
   handling current file.

8. Moved snippet configuration into lsp-mode from company-lsp since snippet
   support will be needed as part of implementing snippet support in lsp-mode Snippet support in completion-at-point #350.
   Aa a result it was possible to clean registration related methods since they
   where used only by company-lsp.

9. Added the option each client to define the location of its libraries and thus
   avoid starting LSP servers for library folders.

10. Method selection based on the configuration in lsp-method->capabilities.

Sample client implementation:

(lsp-register-client
 (make-lsp-client
  :new-connection (lsp-stdio-connection "pyls")
  :major-modes '(python-mode)
  :server-id 'pyls
  :library-folders-fn (lambda (_workspace)
                        (list "/usr/"))))

[FirstLoveLife]

lsp-ui-peek-jump-backward/forward will mess up when opening multiples projects in different workspaces(persp-mode + ccls). For example,

1. projectA:lsp-ui-peek-jump-forward
2. switch to projectB workspace/buffers
3. projectB: lsp-ui-peek-jump-forward
4. return to projectA workspace/buffers
5. lsp-ui-peek-jump-backward => jump into projectB's buffers, which is not what I want.

Can lsp-session fix this problem?

Thanks in advance.

[yyoncho]

@FirstLoveLife I will have to take a look what is causing that issue. For the record, I am using C-o/C-i and they work fine for moving backward/forward after jumping. If the problem is caused by per project jump ring I guess it would be possible to solve if it is moved in lsp-session since it will contain multiple sessions.

[vibhavp]

I still haven't examined all of this, unfortunately. Thanks for submitting this, I'll be sure to have a complete review ready by next week.

[yyoncho]

@vibhavp thanks, it still not 100% ready, some parts are missing, I have posted it only for reviewing the general idea. I do a PR for lsp-ui and company-lsp which do work with this CL. I will ping you when it it ready to be tried. As a side note, should be reviewed from the bottom up.

[MaskRay]

Since merging lsp-*.el is a separate step, can you create a separate PR/commit for it? I'm totally fine with it. That will make the diff smaller and easier to review.

[yyoncho]

I will try to do that. Not sure whether this is going to result in better diff.

[MaskRay]

If this merges the existing lsp-*.el files, LG

[tsoernes]

How do I make use of this?
I want to use both pyls and pyright LSP servers for Python. They do different functions.
I've tried to do

       (python            ; beautiful is better than ugly
        +lsp
        +pyright
        )

In my init.el but pyright is not enabled.