Convert MLOperand methods into readonly attributes

[a-sully]

Fixes #666

Implements the changes proposed in #666 (comment) while simplifying the declaration of these getters to use the pattern suggested in https://webidl.spec.whatwg.org/#idl-frozen-array

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[a-sully]

@fdwr this PR follows up on our recent thread on #666. I expect to migrate the Chromium implementation in the same way as the dimensions -> shape refactoring. PTAL?

[a-sully]

I expect to migrate the Chromium implementation in the same way as the dimensions -> shape refactoring. PTAL?

Hmm unfortunately this style of migration may not be possible in this case, since the Blink bindings code doesn't support interfaces which have a method and an attribute of the same name. See the crashes in https://crrev.com/c/5975719

We can have getters or methods, but not both at the same time... so a migration period is not possible :/

Would you prefer to make this change now or later?

[fdwr]

We can have getters or methods, but not both at the same time... so a migration period is not possible :/

Would you prefer to make this change now or later?

Well I'd like to frontload any breaking changes sooner than later, which smoothens the path to origin trial. However, if we can't mitigate this in any way on the Chromium end, can we closely synchronize the changes by having the corresponding update in samples already ready before completing the Chromium change?

@ibelem : For the ORT-based samples, maybe we could update the sample logic to map a given Chromium version to a correspondingly compatible build of ORT, so there is implicitly a window of migration in the sample logic?

[huningxin]

LGTM

/cc @Honry @BruceDai for required changes in webnn-samples, webnn-baseline and tests.

[fdwr]

👍