[release/9.0] Apply schema transformer to AdditionalProperties

[github-actions]

Backport of #59699 to release/9.0

/cc @captainsafia@JTeeuwissen

Description

This pull request invokes the schema transformer to the AdditionalProperties field within the JSON schema.

Fixes#59616

Customer Impact

This change is necessary to ensure the schema transformer correctly applies to AdditionalProperties, a sub-field within the JSON schema.

While there are workarounds for this issue, the workarounds require the user to implement an extensive amount of custom code in order to properly recurse into an AdditionalProperties subschemas for a given type.

Regression?

• Yes
• No

Risk

• High
• Medium
• Low

Low risk because:

• Change is localized to Microsoft.AspNetCore.OpenApi package
• Change is additive and doesn't change existing behavior

Verification

• Manual (required)
• Automated

Packaging changes reviewed?

• Yes
• No
• N/A

[captainsafia]

Approved via email.