Per #131: Rework how workspace symbol cache is searched and organized

* eglot (eglot--workspace-symbols-cache):  Move closer to point of usage.
Don't clear on every command.
(eglot--recover-workspace-meta): Be aware of minibuffer.el improper lists.
(eglot--pre-command-hook): Simplify.
(xref-backend-identifier-completion-table): Clear cache here.

eglot.el

@@ -2101,12 +2101,8 @@ THINGS are either registrations or unregisterations (sic)."
                               :key #'seq-first))))
       (eglot-format (point) nil last-input-event))))
 
-(defvar eglot--workspace-symbols-cache (make-hash-table :test #'equal)
-  "Cache of `workspace/Symbol' results  used by `xref-find-definitions'.")
-
 (defun eglot--pre-command-hook ()
   "Reset some temporary variables."
-  (clrhash eglot--workspace-symbols-cache)
   (setq eglot--last-inserted-char nil))
 
 (defun eglot--CompletionParams ()
@@ -2396,9 +2392,13 @@ Try to visit the target file for a richer summary line."
           (eglot--current-server-or-lose))
     (xref-make-match summary (xref-make-file-location file line column) length)))
 
+(defvar eglot--workspace-symbols-cache (make-hash-table :test #'equal)
+  "Cache of `workspace/Symbol' results  used by `xref-find-definitions'.")
+
 (cl-defmethod xref-backend-identifier-completion-table ((_backend (eql eglot)))
   (if (eglot--server-capable :workspaceSymbolProvider)
       (let ((buf (current-buffer)))
+        (clrhash eglot--workspace-symbols-cache)
         (cl-labels ((refresh (pat)
                       (mapcar
                        (lambda (wss)
@@ -2457,8 +2457,10 @@ Try to visit the target file for a richer summary line."
   "Search `eglot--workspace-symbols-cache' for rich entry of STRING."
   (catch 'found
     (maphash (lambda (_k v)
-               (let ((probe (member string v)))
-                 (when probe (throw 'found (car probe)))))
+               (while v
+                 ;; Like mess? Ask minibuffer.el about improper lists.
+                 (when (equal (car v) string) (throw 'found (car v)))
+                 (setq v (and (consp v) (cdr v)))))
              eglot--workspace-symbols-cache)))
 
 (add-to-list 'completion-category-overrides