webnn: Give an MLBuffer an MLOperandDescriptor

This CL gives MLBufferDescriptor an MLOperandDescriptor as per
webmachinelearning/webnn#542

To represent this descriptor, this CL also creates a new typemapped
OperandDescriptor type which ensures that the buffer descriptor is
valid. OperandDescriptor will be used more pervasively within WebNN
in follow-up CLs

1) Move Operand::DataType to DataType (MERGED)
2) Create a typemapped OperandDescriptor class for MLBuffer <-- this CL
3) Use OperandDescriptor in mojom::Operand
4+) Remove duplicate code (especially with //components)

Fuchsia binary size seems to be unavoidable for now, and I suspect
may be temporary once duplicate code is removed in follow-ups.
bloaty shows a binary size increase primarily in
//t/b/r/m/ml/webnn/ml_graph_type_converter.cc, as well as a handful
of other renderer-side files which depend on the mojom component

Bug: 343638938, 325598628
Fuchsia-Binary-Size: See commit description
Cq-Include-Trybots: luci.chromium.try:win11-blink-rel
Change-Id: I775340f5c5e0e80942332cbae750d0d305cdd458

webnn/conformance_tests/buffer.https.any.js

@@ -3,6 +3,7 @@
 // META: variant=?cpu
 // META: variant=?gpu
 // META: variant=?npu
+// META: script=../resources/utils_validation.js
 // META: script=../resources/utils.js
 // META: timeout=long
 
@@ -11,7 +12,18 @@
 // https://webmachinelearning.github.io/webnn/#api-mlbuffer
 
 if (navigator.ml) {
-  testCreateWebNNBuffer('create', 4);
+  testCreateWebNNBuffer('create', {dataType: 'float16', dimensions: [2, 3]});
+  testCreateWebNNBuffer('create', {dataType: 'float32', dimensions: [1, 5]});
+  testCreateWebNNBuffer('create', {dataType: 'int32', dimensions: [4]});
+  testCreateWebNNBuffer('create', {dataType: 'uint8', dimensions: [3, 2, 4]});
+
+  testCreateWebNNBufferFails(
+      'createFailsEmptyDimension', {dataType: 'int32', dimensions: [2, 0, 3]});
+  testCreateWebNNBufferFails('createFailsTooLarge', {
+    dataType: 'int32',
+    dimensions: [kMaxUnsignedLong, kMaxUnsignedLong, kMaxUnsignedLong]
+  });
+
   testDestroyWebNNBuffer('destroyTwice');
   testReadWebNNBuffer('read');
   testWriteWebNNBuffer('write');