@W-23818035 feat: AsyncAPI 3.0/3.1 field-level rendering support

[looseale]

Splits the AsyncAPI portion of the original combined new-spec effort (W-23597071) into its own branch.

Adds AsyncAPI 3.0 / 3.1 field-level rendering: send/receive action labels (colored as publish/subscribe), and message payload discovery via operationMessages/channelMessages. See the status doc docs/superpowers/W-23818035-async-new-spec-support.md in anypoint-api-console.

NOTE: this branch is stacked on the OAS branch (W-23818022). Because it is submitted from a fork, the PR targets the default branch and therefore includes the OAS commits as well; once the OAS PR merges, only the async diff will remain.

Issue: W-23818035

Submitted from fork looseale/<repo>.

[salesforce-cla]

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[salesforce-cla]

Thanks for the contribution! Before we can merge this, we need @looseale to sign the Salesforce Inc. Contributor License Agreement.