Session.open_uri_async: Focus view when open file: URI

[LDAP]

Closes #2078

Session.open_uri_async focuses a view if there is a preexisting session buffer: https://github.com/sublimelsp/LSP/blob/969a9c8d8f581f4815643b3297501cb55b49a1d9/plugin/core/sessions.py#L1487-L1490 or if the URI was opened using a plugin, since in this case the view was newly created: https://github.com/sublimelsp/LSP/blob/969a9c8d8f581f4815643b3297501cb55b49a1d9/plugin/core/sessions.py#L1531-L1534 However, when the URI starts with file: then the view is only focused if the file was previously not open.