* Update release number to 87.
Public Issues:
* Merge flink:vkCmdPipelineBarrier self-dependency barrier VUs referring
to the same subpass dependency (public pull request 756).
* Describe default value of `"optional"` attribute in the registry schema
document (public issue 769)
* Fix links in <<VK_NVX_raytracing>> extension (public pull request 805).
* Mark the <<VK_KHR_mir_surface>> extension obsolete (see public issue 814
- does not close this, however).
* Fix missing endif in Image Creation block (public issue 817).
Internal Issues:
* Clarify that the compressed texture formats corresponding to
<<features-features-textureCompressionETC2>>,
<<features-features-textureCompressionASTC_LDR>>, and
<<features-features-textureCompressionBC>> is not contingent on the
feature bits, and may be supported even if the features are not enabled
(internal issue 663).
* Clarify that code:FragStencilRefEXT is output only in the
<<interfaces-builtin-variables, Built-In Variables>> section (internal
issue 1173).
* Identify and correct many overly-aggressive uses of "`undefined`", and
narrow them down, where straightforward to do so. Mark such resolved
uses of "`undefined`" with the custom undefined: macro. Add a new
<<writing-undefined, Describing Undefined Behavior>> section (internal
issue 1267).
* Don't require code:inline_uniform_block descriptors to be populated
before use in the flink:vkAllocateDescriptorSets section (internal issue
1380).
* Allow suppressing inline SVG images by controlling this with an
attribute set in the Makefile, rather than the explicit [%inline]
directive (internal issue 1391).
* Mark 'Khronos' as a registered trademark in several places, now that it
is one.
* Fix typo in the <<VK_KHR_shader_atomic_int64>> appendix using the GLSL
naming of the compare exchange op when referring to the SPIR-V op.
* Specify in the flink:vkGetPhysicalDeviceQueueFamilyProperties section
that all implementations must support at least one queue family, and
that every queue family must contain at least one queue.
* Make slink:VkPipelineDynamicStateCreateInfo::pname:dynamicStateCount,
slink:VkSampleLocationsInfoEXT::pname:sampleLocationsPerPixel, and
slink:VkSampleLocationsInfoEXT::pname:sampleLocationsCount optional, to
fix bogus implicit valid usage checks that were causing failures in the
conformance tests.
* Fix vendor tag in reserved extension 237 constants. Does not affect
anything since it's just a placeholder, but this should avoid further
comments.
* Minor markup fixes in some extension appendices.
New Extensions:
* `<<VK_FUCHSIA_imagepipe_surface>>`
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