Merge RC2 into 9.3 (actually-stable)

See merge request !2122

Fix all 9-3-stable-ee spec failures

See merge request !2095

These specs differ a bit between CE and EE to make things easier.

Rework project authorizations and nested groups for better performance

See merge request !10885

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Fix typo in moving the`appearance` folder in migrations

See merge request !2116

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Move the uploads in the correct folder when moving project/namespace

See merge request !2112

Fix visibility when referencing snippets

See merge request !2101

Move the uploads in the correct folder when moving project/namespace

See merge request !2112

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