Move release notes from 1.21 to 1.22

Several change sets that added entries to RELEASE-NOTES-1.21 were
actually submitted after the REL1_21 branch point. Those change
sets that are unlikely to be backported to 1.21 (i.e. not yet
backported) are listed here.

* I0f2d81dd (bug 23393) (bug 45803)
* I226349aa
* I3faa9c3e (bug 23343)
* I6e7f4cf6
* I719d84c5
* I97b04673
* Ia98f54f4
* Idab489fc (bug 25325)
* Ifaf40c66 (bug 46680)

This patch moves the release notes to the RELEASE-NOTES-1.22 file.

Change-Id: I6a51e3ee07fe7622b9c708c78563795d7a1118fc