Move all existing global routes under /-/ scope

Like #29572 (closed) but for global routes.

The problem was raised in gitlab-foss#61985 (moved)

Example.

We have notification_settings route that is a reserved work in TOP_LEVEL_ROUTES. It can be easily put under - scope and remove reserve word. This will increase performance of every route as it reduce the size of regex that is build from TOP_LEVEL_ROUTES.

TODO:

12.9

• Move notification_settings => !26983 (merged)

12.10

• Move abuse_reports, invites, sent_notifications => !27106 (merged)
• Move autocomplete routes => !30173 (merged)

13.2

• Copy snippet routes under /-/ scope. !35020 (merged)

13.3

• Make snippet routes under /-/ as default one. !36091 (merged)

13.5

• Copy profile routes under /-/ scope. !45045 (merged)

13.6

• Make profile routes under /-/ as default one. !45307 (merged)

14.0

• Redirect /snippets to /-/snippets. Except raw. !54461 (merged)

Unplanned

• Move clusterable, search, users etc

Removing deprecated routes

Should be handled in separate issue => #28848 (closed)