SECURITY: Act like users don't exist if hidden from viewer
b5e7f210cd31
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Description

SECURITY: Act like users don't exist if hidden from viewer

When viewing Special:Contributions for a hidden user and
a missing user, or the user page of a hidden user and a
missing user, if the viewer cannot see hidden users
the output should be the same for hidden users and
missing users.

To that end

In OutputPage.php, only set the wgRelevantUserName javascript variable if the user is not hidden, or the viewer can see hidden users
In Article.php, show the userpage-userdoesnotexist-view on user pages of hidden users if the viewer cannot see hidden users
In Skin.php, do not add user-specific sidebar links (contributions, logs, mute, etc.) if the user is hidden and the viewer cannot see hidden users
In SpecialContributions.php, stop calling Skin::setRelevantUser for non-existing users, so that callers of Skin::getRelevantUser can ignore users that are hidden from the viewer without creating divergent behavior
In SpecialContributions.php, for users that do exist but are hidden from the viewer, don't show sp-contributions-footer, but do show contributions-userdoesnotexist

Bug: T120883
Change-Id: I83b723402f315447bc4b50992e28620e3daace8f