cl_khr_command_buffer_mutable_dispatch (#819)

* cl_khr_command_buffer_mutable_dispatch

Add extension spec for provisional extension
`cl_khr_command_buffer_mutable_dispatch`, which is layered on top
of `cl_khr_command_buffer`.

This extension allows a user to update kernel execution commands
recorded to a command-buffer between kernel enqueues.

Added at bottom of `OpenCL_Ext` extension list, rather than next
to entry for `cl_khr_command_buffer` to avoid reordering the section
numbers of the following extensions.

* Apply suggestions from code review

Change `_dispatch_` to `_command_` in `clGetMutableCommandInfoKHR` table, and specify global work size will return zero if not set

Co-authored-by: Alastair Murray <alastair.murray@codeplay.com>

Co-authored-by: Alastair Murray <alastair.murray@codeplay.com>

Author: EwanC

OpenCL_Ext.txt

@@ -106,6 +106,8 @@ include::ext/cl_khr_expect_assume.asciidoc[]
 include::ext/cl_khr_subgroup_rotate.asciidoc[]
 include::ext/cl_khr_work_group_uniform_arithmetic.asciidoc[]
 
+include::ext/cl_khr_command_buffer_mutable_dispatch.asciidoc[]
+
 // NOTE: To keep meaningful section numbers, new
 // extension documents should be added above here!
 

ext/cl_khr_command_buffer.asciidoc

@@ -559,6 +559,7 @@ supported property and its value is not specified in properties, its
 default value will be used. _properties_ can be `NULL` in which case the
 default values for supported command-buffer properties will be used.
 
+[[commandbuffer-properties]]
 .*clCreateCommandBufferKHR* properties
 [cols=",,",options="header",]
 |====
@@ -573,7 +574,7 @@ default values for supported command-buffer properties will be used.
   `CL_COMMAND_BUFFER_SIMULTANEOUS_USE_KHR` - Allow multiple instances of the
   command-buffer to be submitted to the device for execution. If set, devices
   must support `CL_COMMAND_BUFFER_CAPABILITY_SIMULTANEOUS_USE_KHR`.
-  
+
   The default value of this property is `0`.
 |====