[modeline] Add segments to future drop global-mode-string

[ericdallo]

Fixes #2571

This PR adds 2 new variables:

• lsp-modeline-use-global-mode-string with t as default which behaves the same as ATM, adding modeling strings to the global-mode-string.
• lsp-modeline-segments used in case lsp-modeline-use-global-mode-string is nil, indicating the modeling segments features and its order, adding those segments in the mode-line-format before major modes following the same evil-mode does.

This should standardize the way we add things to modeling and make it easy to improve fixing spacing and other things.

To disable lsp-modeline-use-global-mode-string by default, we should at least update major modelines like doom-emacs modeline, doom-modeline, spaceemacs (?) to use the lsp-modeline--string in their modeling.

How it looks on my modeline:

[ericdallo]

c/c @yyoncho @alanz @kiennq