gpu: add dawn.EncoderInternalUsageDescriptor

Signed-off-by: Stephen Gutekanst <stephen@hexops.com>

gpu/src/dawn.zig

@@ -5,3 +5,9 @@ pub const CacheDeviceDescriptor = struct {
     chain: ChainedStruct,
     isolation_key: [*:0]const u8,
 };
+
+pub const EncoderInternalUsageDescriptor = struct {
+    // TODO: file an issue on Dawn: why not named nextInChain?
+    chain: ChainedStruct,
+    use_internal_usages: bool,
+};