[core] core-client-rest PathUnchecked does not infer path parameters which are not preceded by /

[timovv]

Example (made by generating the Batch modular SDK from TypeSpec when using pathUnchecked instead of path):

export function _deleteCertificateSend(
  context: Client,
  thumbprintAlgorithm: string
  thumbprint: string,
  options: DeleteCertificateOptionalParams = { requestOptions: {} },
): StreamableMethod {
  return context
    .pathUnchecked(
      "/certificates(thumbprintAlgorithm={thumbprintAlgorithm},thumbprint={thumbprint})",
      thumbprintAlgorithm,
      thumbprint,
    )
    .delete({
      ...operationOptionsToRequestParameters(options),
      queryParameters: {
        "api-version": options?.apiVersion ?? "2023-05-01.17.0",
        timeOut: options?.timeOutInSeconds,
      },
    });
}

There are two URL parameters, so the function should accept 3 arguments, but compilation fails with:

src/api/operations.ts:6972:7 - error TS2554: Expected 1 arguments, but got 3.

6972       thumbprintAlgorithm,
           ~~~~~~~~~~~~~~~~~~~~
6973       thumbprint,
     ~~~~~~~~~~~~~~~~

This is because the definition of PathParameters in @azure/core-client-rest assumes that each path parameter is preceded immediately by a /. This is not necessarily true, as in this example. Because of this assumption, the type helper indicates that this path has 0 path parameters, when in reality it has 2.

There is no actual runtime impact since the algorithm that actually fills in the template with the values doesn't care if the template parameter is preceded by a / or not.

If possible, we should update the type definition of PathParameters to accommodate this scenario.