Fix https://gitlab.com/gitlab-org/gitlab-ce/issues/40671

See
https://gitlab.com/gitlab-org/gitlab-ce/blob/f7254a4060b30e3134c6cf932eaba0fc8e249e9a/app/controllers/sessions_controller.rb#L42
for an example of where we set `flash[:notice] = nil`

When checking if a branch is protected we don't need all columns of
every protected branch row, instead we only care about the names. By
using "select" here we reduce the amount of data we need to send over
the wire and load into memory.

Before the we would try to `POST` to the project path, which would
result in a 404, because that `POST` is not supported.

By changing this back to a normal link, not not handled in JS, we can
immeadiatly redirect.

this is not a great way to do this. But using currentColor for these
means we are competing with this selector:
 ul.content-list li a

[ci-skip]

Fix https://gitlab.com/gitlab-org/gitlab-ce/issues/38962

Fix https://gitlab.com/gitlab-org/gitlab-ce/issues/38962

If a merge request was created with a branch name that also matched a tag name,
we'd generate a comparison to or from the tag respectively, rather than the
branch. Merging would still use the branch, of course.

To avoid this, ensure that when we get the branch heads, we prepend the
reference prefix for branches, which will ensure that we generate the correct
comparison.

Fix https://gitlab.com/gitlab-org/gitlab-ce/issues/40373

When copying some text from another note and paste,
it goes through `copy_as_gfm` `paste` handler
that calls `e.preventDefault()` which stops things.
But then when inserting the text, we manually trigger
an `input` event with jQuery which doesn't seem to be
picked up by Vue `v-model`.

Using copy/paste trick from https://stackoverflow.com/a/41046276/796832

The st_commits and st_diffs columns on merge_request_diffs historically held the
YAML-serialised data for a merge request diff, in a variety of formats.

Since 9.5, these have been migrated in the background to two new tables:
merge_request_diff_commits and merge_request_diff_files. That has the advantage
that we can actually query the data (for instance, to find out how many commits
we've stored), and that it can't be in a variety of formats, but must match the
new schema.

This is the final step of that journey, where we drop those columns and remove
all references to them. This is a breaking change to the importer, because we
can no longer import diffs created in the old format, and we cannot guarantee
the export will be in the new format unless it was generated after this commit.

Previously we'd use "event.author_email" which translates to
"event.author.email". This would result in an extra query being executed
_for every event_ just to get the same author's Email address.

Instead of doing all this useless work we can just pass the User object
returned by "event.author" since:

1. This allows us to re-use the user object's Email address.
2. Authors are eager-loaded, so this doesn't cause any N+1 queries.