Accept functions as entries in eglot-server-programs

CONTACT in the (MAJOR-MODE . CONTACT) association in
eglot-server-programs can now be a function of no arguments producing
any value previously valid for contact.  The function is called at
time of `M-x eglot` or `eglot-ensure`.  This is useful for servers
requiring command-line invocations that depend on the specific
momentary environment.

* eglot.el (eglot-server-programs): CONTACT can be a fucntion of no
arguments.
(eglot--guess-contact, eglot--connect): Accept function
CONTACTs.

GitHub-reference: per joaotavora/eglot#63

lisp/progmodes/eglot.el

@@ -121,7 +121,10 @@ of those modes.  CONTACT can be:
   converted to produce a plist with a suitable :PROCESS initarg
   to CLASS-NAME.  The class `eglot-lsp-server' descends
   `jsonrpc-process-connection', which you should see for the
-  semantics of the mandatory :PROCESS argument.")
+  semantics of the mandatory :PROCESS argument.
+
+* A function of no arguments producing any of the above values
+  for CONTACT.")
 
 (defface eglot-mode-line
   '((t (:inherit font-lock-constant-face :weight bold)))
@@ -310,6 +313,7 @@ be guessed."
                             (lambda (m1 m2)
                               (or (eq m1 m2)
                                   (and (listp m1) (memq m2 m1)))))))
+         (guess (if (functionp guess) (funcall guess) guess))
          (class (or (and (consp guess) (symbolp (car guess))
                          (prog1 (car guess) (setq guess (cdr guess))))
                     'eglot-lsp-server))
@@ -457,6 +461,7 @@ This docstring appeases checkdoc, that's all."
          (nickname (file-name-base (directory-file-name default-directory)))
          (readable-name (format "EGLOT (%s/%s)" nickname managed-major-mode))
          autostart-inferior-process
+         (contact (if (functionp contact) (funcall contact) contact))
          (initargs
           (cond ((keywordp (car contact)) contact)
                 ((integerp (cadr contact))
@@ -1658,7 +1663,7 @@ If SKIP-SIGNATURE, don't try to send textDocument/signatureHelp."
   "Passes through required cquery initialization options"
   (let* ((root (car (project-roots (eglot--project server))))
          (cache (expand-file-name ".cquery_cached_index/" root)))
-    (list :cacheDirectory (file-name-as-directory cache)
+    (list :cacheDirectory (file-name-as-directory cache)Ini
           :progressReportFrequencyMs -1)))