Rename 'type' field to 'operation'.

This CL is a step towards getting fetch API changes from the Private
State Token (PST, formerly known as TrustTokens) explainer. After
this CL fetch API will be as follows.

fetch('<issuer>/<issuance path>', {
  trustToken: {
    operation: 'token-request',
    issuer: <issuer>
  }
}).then(...)

Ultimately, we would like to be compatible with the explainer and have
the fetch API as follows.

fetch('<issuer>/<issuance path>', {
  privateToken: {
    type: 'private-state-token',
    version: 1,
    operation: 'token-request',
    issuer: <issuer>
  }
}).then(...)

This API creates room for supporting new type of tokens with backward
compatibility. It also supports having different versions of the PST coexist.

The edits in this CL stems from the the following two sources.

- In ./services/network/public/mojom/trust_tokens.mojom: Rename
  TrustTokenParams's 'type' field to 'operation'. Rename
  TrustTokenOperationResult's 'type' field to 'operation'.

- In ./thirdparty/blink/renderer/core/fetch/trust_token.idl: Rename
  'type' to 'operation'.

Bug: 1404729
Fixed: 1404730
Explainer: https://github.com/WICG/trust-token-api
Spec: https://wicg.github.io/trust-token-api/
Change-Id: I4742bd8e24c4437f35f6d2ccc08caf9dab7ae139
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4126918
Reviewed-by: Yoav Weiss <yoavweiss@chromium.org>
Reviewed-by: Matt Menke <mmenke@chromium.org>
Commit-Queue: Aykut Bulut <aykutb@google.com>
Reviewed-by: Russ Hamilton <behamilton@google.com>
Reviewed-by: Steven Valdez <svaldez@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Reviewed-by: Dominic Farolino <dom@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1094573}