Allow lsp languageid to be overridden via eglot-server-programs

Allow lsp languageid to be overridden via eglot-server-programs

Close https://github.com/joaotavora/eglot/issues/678. Per https://github.com/joaotavora/eglot/issues/677

* eglot-tests.el (eglot--guessing-contact): Add
GUESSED-LANG-ID-SYM param.
(eglot-server-programs-guess-lang): New test.

* eglot.el (eglot-server-programs): Augment entries for caml-mode
and tuareg-mode. Enhance docstring.
(eglot--lookup-mode): New helper.
(eglot--guess-contact): Call eglot--lookup-mode.
(eglot, eglot-reconnect): Pass language-id to eglot--connect
(eglot--connect): Receive LANGUAGE-ID
(eglot--TextDocumentItem): Simplify.  Use
`eglot--current-server-or-lose'

* README.md (Handling quirky servers): Mention new feature.

Co-authored-by: João Távora <joaotavora@gmail.com>