increased perf of scrolling tabs into view

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[ci skip]

scroll to the active tab when opening/closing

[ci skip]

removed an ID from the CSS

Encompasses designs from
 - https://gitlab.com/gitlab-org/gitlab-ce/issues/23206#note_43355199
 - https://gitlab.com/gitlab-org/gitlab-ce/issues/29985#note_30417407

This moves away from storing in a single array just to render the table.
It now stores in a multi-dimensional array/object type where each entry
in the array can have its own tree. This makes storing the data for
future feature a little easier as there is only one way to store the
data.

Previously to insert a directory the code had to insert the directory
& then the file at the right point in the array. Now the directory
can be inserted anywhere & then a file can be quickly added into this
directory.

The rendering is still done with a single array, but this is handled
through underscore. Underscore takes the array & then goes through
each item to flatten it into one. It is done this way to save changing
the markup away from table, keeping it as a table keeps it semantically
correct.

Fix https://gitlab.com/gitlab-org/gitlab-ce/issues/38315
Fix https://gitlab.com/gitlab-org/gitlab-ce/issues/38187

- Cleans the fork project layout by removing the grid & reverting back
to full flexbox to allow for the layout to correctly expand.
- Removes duplicated markup
- Fixes a bug where the forked project would trigger the load indicator

FE for https://gitlab.com/gitlab-org/gitlab-ce/issues/34102

Previously the fork button was disabled for all users if they have
exceeded their project limit. This fixes that by changing the check
to see if the user can fork to a group instead of their own namespace.

This behaviour is already possible by visiting the new fork page
directly, so this just fixes the button being disabled.

Closes #38462