lsp: Add support for external document show (showDocument param :external?) (#4872)

* Add support for external document show

This change enhances lsp--window-show-document to handle external URLs by:
- Adding external? parameter support from ShowDocumentParams
- Opening external URIs in browser via browse-url
- Maintaining existing file-based document handling

* lsp: response t if we can show document in external browser

* style: indentation

---------

Co-authored-by: JenChieh <[email protected]>

Author: yuansl

lsp-mode.el

@@ -2226,14 +2226,18 @@ PARAMS - the data sent from WORKSPACE."
         (completing-read (concat message " ") (seq-into choices 'list) nil t)
       (lsp-log message))))
 
-(lsp-defun lsp--window-show-document ((&ShowDocumentParams :uri :selection?))
-  "Show document URI in a buffer and go to SELECTION if any."
+(lsp-defun lsp--window-show-document ((&ShowDocumentParams :uri :selection? :external?))
+  "Show document URI in a buffer or in a external browser if EXTERNAL is t, and go to SELECTION if any."
   (let ((path (lsp--uri-to-path uri)))
-    (when (f-exists? path)
-      (with-current-buffer (find-file path)
-        (when selection?
-          (goto-char (lsp--position-to-point (lsp:range-start selection?))))
-        t))))
+    (if external?
+        (progn
+          (browse-url uri)
+          t)
+      (when (f-exists? path)
+        (with-current-buffer (find-file path)
+          (when selection?
+            (goto-char (lsp--position-to-point (lsp:range-start selection?))))
+          t)))))
 
 (defcustom lsp-progress-prefix "⌛ "
   "Progress prefix."