* Update release number to 89.
Public Issues:
* Clarify the reference to <<features-limits-mipmapPrecisionBits, mipmap
precision bits>> in the <<textures-image-level-selection, Image Level(s)
Selection>> section (public issue 660).
* Update <<debugging-object-types,VkObjectType and Vulkan Handle
Relationship>> table with missing types (public pull request 820).
* Miscellaneous minor markup cleanup (public pull request 822).
* Fix copy/paste bugs in the description of how implicit
availability/visibility operations for atomics/barriers are ordered in
the <<memory-model-availability-visibility-semantics, Availability and
Visibility Semantics>> section (public issue 823).
* Add missing shading_rate_image bit from mesh pipeline list in the
<<synchronization-pipeline-stages-types>> list (public issue 824).
Internal Issues:
* Clarify that only statically used members of a push constant block need
to be in the push constant range, and stop referring to block members as
"`variables`" in the <<interfaces-resources-pushconst, Push Constant
Interface>> section. This is related to
https://github.com/KhronosGroup/Vulkan-ValidationLayers/issues/340
(internal issue 1401).
* Clarify interaction between flink:vkCmdSetDeviceMask and render pass
control commands in the slink:VkDeviceGroupRenderPassBeginInfo section
(internal issue 1416).
* Miscellaneous minor markup cleanup.
* Remove types defined by `"disabled"` extensions from
validextensionstructs in the XML processing scripts, so downstream code
generators don't emit them.