feat: provide a sync button in the preview panel

[Myriad-Dreamin]

When a client doesn't implement the bidirectional jumping feature (lsp notifications), a sync button is used as a fallback solution. This is useful, because a client, like helix and zed, usually cannot handle these bidirectional jump notifications.

The sync button works in this way:

• when user triggers a hover and completion, the server remembers it.
• when user presses the sync button, the server request to jump a document location in preview corresponding to the source location held in the last step.
• the preview panel can optionally render the source location for help.