Show Metals treeview associated with current buffer filename.

Fix a bug with multiple workspaces, when closing one workspace
the treeview will be closed. When a file associated with the closed
workspace was open and invoking lsp-metals-treeview the other
workspace's treeview would be displayed.
lsp-metals-treeview now uses lsp-find-workspace with metals
server-id and filename of current buffer to locate the
associated workspace.

Author: dsyzling

lsp-metals-treeview.el

@@ -826,7 +826,8 @@ the current buffer."
   (interactive)
   (-if-let* ((workspace
               (or workspace
-                  (lsp-find-workspace lsp-metals-treeview--metals-server-id nil))))
+                  (lsp-find-workspace lsp-metals-treeview--metals-server-id
+                                      (buffer-file-name)))))
       (lsp-metals-treeview--show-window workspace t)
     (message "Current buffer is not within Metals workspace")))