Support legacy behavior for --host-vmservice-port and --observatory-port with DDS (#70336)

Implements the following:
  - If both --host-vmservice-port and --dds-port are specified, use the current behavior
  - If only --host-vmservice-port is specified and dds is enabled, use that for the dds port
  - If only --dds-port is specified, use that for the dds port

Fixes https://github.com/flutter/flutter/issues/70332