release 1.9.0

[kusma]

1.9.0-rc1:

• [x] Verify all previous release-branch has been merged.
• [x] Verify that CHANGELOG.md is OK.
• [x] Create release-branch.
• [x] Protect release-branch.
• [x] Update version number.
• Upload packages:
  • [x] upload/FuseOpen.Uno.*.nupkg
  • [x] upload/Uno.*.upk
  • [x] upload uno.packages to the GitHub releases
• [x] Merge to master.

1.9.0 (final):

• [x] Ensure all reported regressions are addressed
• [x] Update version number.
• [x] Update release-branch and tag.
• Upload packages:
  • [x] upload/FuseOpen.Uno.*.nupkg
  • [x] upload/Uno.*.upk
  • [x] upload uno.packages to the GitHub releases
• [x] Merge to master.

(based on the release guide)

[kusma]

Done.