Scroll to anchor when blob content is loaded

Fixes bug introduced by https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/10566.

Because Markdown blob content is now loaded asynchronously, anchors like https://gitlab.com/gitlab-org/gitlab-ce/blob/master/README.md#installation would no longer be automatically scrolled to.

approved this merge request

assigned to @DouweM

@DouweM Change looks good, pls take a look at the tests, look unrelated to me but leaving the merge to you

merged

mentioned in commit b957df95

mentioned in issue #32437 (closed)

mentioned in commit 46199016

@timzallmann: This MR doesn't merge cleanly onto 9-2-stable. I've created an MR for this ( https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/11484 ) - could you please resolve the conflicts there?

mentioned in merge request !11484 (merged)