[Bug][http] can't declare requiredness for meta properties about file part of multipart

[msyyc]

According to #3046, httpFile could be used to change the requiredness of the optional metadata properties

However, when I try the following code, I find the type is Scalar bytes which contains no info about "contentType"/"filename" is required for this file part.

  it("test", async () => {
    const op = await getHttpOp(`

    @Private.httpFile
    model RequiredFileMetadata {
      contentType: string;
      filename: string;
      contents: bytes;
    }
      op read(
        @header contentType: "multipart/mixed",
        @multipartBody body: [
          HttpPart<RequiredFileMetadata, #{ name: "file" }>
        ]): void;
    `);

    const body = op.parameters.body;
    strictEqual(body?.bodyKind, "multipart");
  });

[timotheeguerin]

hhm yeah seems like I didn't handle HttpFile completely