Support wasm backend

[Honry]

Delivers wasm binaries to dist/ foloder for wasm backend.

[Honry]

@BruceDai, @huningxin, PTAL, thanks!

[BruceDai]

Thanks @Honry.

I verified locally on browser http://127.0.0.1:8080/test/?backend=wasm with workload

--- a/src/nn/context.ts
+++ b/src/nn/context.ts
@@ -63,7 +63,7 @@ export class MLContext {
   get tf(): unknown {
     // Set directory of wasm binaries for 'wasm' backend
     wasm.setWasmPaths(
-        'https://webmachinelearning.github.io/webnn-polyfill/dist/');
+        'http://127.0.0.1:8080/dist/');
     return tf;
   }
 }

Now test result of total 615 tests: passes: 566 failures: 48 pending: 1

The failures tests are

• some conv2d transpose with "AssertionError at checkValue"
• some maxPool2d dilations with "Error: Kernel 'SpaceToBatchND' not registered for backend 'wasm'" which links https://github.com/tensorflow/tfjs/pull/5288
• some resample upsample nearest with "Error: Kernel 'ResizeNearestNeighbor' not registered for backend 'wasm'" which was reported https://github.com/tensorflow/tfjs/issues/4766
• some CTS maxPool2d / averagePool2d with "AssertionError at checkValue" , the error messages are

[Honry]

Thanks @BruceDai ! Are all the failure tests expected for wasm backend?

[Honry]

@huningxin, thanks for your comments, fixed the nits, PTAL again, thanks!

[Honry]

@huningxin, I've updated the PR to reuse the wasm binaries from TensorFlow.js, PTAL, thanks!