[wteja]

Emit required properties for MVC [FromForm] complex models.

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Summary of the changes (Less than 80 chars)

Description

Populate form-schema required lists from MVC binding and property validation metadata. Handle both a single form model and grouped schemas when additional form parameters are present, preserving explicitly renamed form fields.

Add regression coverage for [BindRequired], [Required], a required container parameter, the renamed file_upload field, and optional scalar and nullable properties. Update controller snapshots for OpenAPI 3.0, 3.1, and 3.2, plus the localization snapshot.

Fixes #69943

Testing

Validated on macOS arm64 with the repository SDK 12.0.100-alpha.1.26521.103:

• New regression theory: all 3 cases pass at the PR head and fail at the base commit with the same test file applied. Each base failure reports a missing required list.
• Complete Microsoft.AspNetCore.OpenApi.Tests project: 1,036 passed, 5 existing skips, 0 failed. Includes all 63 document snapshot cases and the localization snapshot.
• Complete Microsoft.AspNetCore.Mvc.ApiExplorer.Test project: 296 passed, 0 failed.

[dotnet-policy-service]

Thanks for your PR, @wteja. Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[wteja]

@dotnet-policy-service agree