Bug 577865 - F3 - open definition on Generic Editor should directly

open the first definition found

Issue: https://bugs.eclipse.org/bugs/show_bug.cgi?id=577865
Issue: https://github.com/eclipse/lsp4e/issues/25

Change-Id: I21213b93a6c38f7130679a983ec8d83888d43c19
Signed-off-by: Victor Rubezhny <vrubezhny@redhat.com>
Reviewed-on: https://git.eclipse.org/r/c/platform/eclipse.platform.text/+/188941
Tested-by: Platform Bot <platform-bot@eclipse.org>
Reviewed-by: Mickael Istria <mistria@redhat.com>