Using concrete class types with static IIDs in QueryInterface methods is a
pretty common pattern which isn't supported by any existing helper macros.
That's lead to separate ad-hoc implementations, with varying degrees of
dodginess, being scattered around the tree.
This patch adds a helper macro with a canonical (and safe) implementation, and
updates existing ad-hoc users to use it.
MozReview-Commit-ID: HaTGF7MN5Cv
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extra : rebase_source : ace930129d85960d22bc3048ca3bb19bbbd4a63e
extra : histedit_source : 03a87f746d957789d41381e4e1bfcc4fd7eebaf2%2C9c5bae9feeeef7721105db67be0f83e0ded66bb7
8340513b0c