Add move operations to EncoderSettings

EncoderSettings declares a copy constructor and a copy assignment
operator, so it has no implicit move operations, and std::move on an
EncoderSettings copies it, including its VideoEncoderConfig and
EncoderInfo. For example, SetEncoderSettings() in
VideoStreamEncoderResourceManager and OnEncoderSettingsUpdated() in
BitrateConstraint take the settings by value and move them into a
member, which made a copy.

Add a defaulted move constructor and move assignment operator. Like the
existing copy operations, they are defined out of line.

Also avoid the two copies made in
VideoStreamEncoder::OnEncoderSettingsChanged():
VideoStreamInputStateProvider only reads the settings, so take them by
const reference in its OnEncoderSettingsChanged(). Call that before
SetEncoderSettings(), which neither reads from nor writes to the input
state provider, so that the settings can be moved into
SetEncoderSettings(). Read the screenshare and zero-hertz flags from
`encoder_config_`, which the settings' config is a copy of.

An encoder settings change now copies EncoderSettings once, into
BitrateConstraint, instead of five times.

Bug: webrtc:374845009
Change-Id: I06419eda299836ae282ef88b95a1a1c6c8a4bb1f
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/507860
Commit-Queue: Fredrik Solenberg <solenberg@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#48821}