Ensure safety of indirect draw/dispatch

[kvark]

When doing an indirect draw, the range of vertices/indices to draw needs to be within the bounds of the active vertex and index buffers. Similarly, indirect dispatches must be within the limits of the workgroup count.

• Ensure safety of indirect dispatch #5714
• Ensure safety of indirect draw
• Enforce a no-op if the device does not have INDIRECT_FIRST_INSTANCE feature enabled.

[kvark]

Here is a rough plan:

1. wgpu-hal expects platform-dependent draw/dispatch buffer.
2. the only thing exposed to the outside is the size of that buffer (for each kind of draw/draw indexed/dispatch)
3. wgpu-hal command encoder gets a new fn prepare_indirect(src_buffer, src_offset, dst_buffer, dst_offset, kind, count). Under the hood it will be a compute operation that does clamping as well as copies of first instance/vertex.
4. wgpu-core spawns a separate encoder to prepare indirect calls whenever it sees one, and orders it accordingly. It also manages the destination buffer as a temporary thing.

[teoxoy]

When we get to this, we should also validate usage of the indirect-first-instance feature.

The value corresponding to firstInstance must be 0, unless the "indirect-first-instance" feature is enabled. If the "indirect-first-instance" feature is not enabled and firstInstance is not zero the drawIndirect() call will be treated as a no-op.

[ErichDonGubler]

I've updated the OP with the scope of remaining changes I'm aware need to happen.

[ErichDonGubler]

Downstream Firefox tracking for indirect dispatch: bug 1921342

[ErichDonGubler]

Downstream Firefox tracking for indirect draws: bug 1930972