Check id entered in SpecialSetSiteLink is an ItemId

(also make capitalisation of "id" more consistent in these special pages)

Bug: 56933
Change-Id: I56c35d06039a34473e09225ffc551da5978a169e
(cherry picked from commit 95a51924c897276c73260c2a76a7eccffc8c520b)
Merge "Check id entered in SpecialSetSiteLink is an ItemId"