Polyfill non-4-byte-aligned fills in the Vulkan HAL. (#7317)

This fixes https://github.com/google/iree/issues/7228 by introducing a new `BuiltinExecutables` class under the Vulkan HAL that uses a 1x1x1 dispatch to fill any unaligned bytes within a buffer fill operation. Aligned regions of buffer fills will still use the native `vkCmdFillBuffer`. New CTS test cases provide coverage for each [pattern_size x offset x fill_length] permutation.

Inserting a dispatch into a command buffer (that was expecting to just have a native `vkCmdFillBuffer` transfer operation inside it) requires some special handling:

* Descriptor set layout index 3 is used (Android typically only supports 4, so this is the last slot), to avoid overlap with descriptor set layouts used by the compiler.
* Push constants are tracked for each command buffer so when this dispatch uses its own push constants it can restore from that backup.
* Command buffers that may go down this polyfill path need to run on a queue compatible with dispatch operations (i.e. not transfer exclusive). We had some ideas for adding a compiler analysis and attribute for "will only contain aligned fills", but without that I'm just defaulting to `command_categories |= IREE_HAL_COMMAND_CATEGORY_DISPATCH` where needed.

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I have not yet tested this in a real program and there are still a few TODOs for optimal performance and correct synchronization behavior.