SF: Remove DisplayDevice::ActiveModeInfo

This type is redundant with DisplayModeRequest, so store the desired and
pending modes as DisplayModeRequestOpt. This is a step toward flowing
the request through one of desired/pending/active states.

Use the std::nullopt state of the desired mode instead of relying on the
implicitly associated TracedOrdinal<bool>.

Bug: 241285876
Test: presubmit
Change-Id: Ie12a5ad420745761c73b1ce2c536862f79a50665