Update ColorScheme.toString() formatting

ThemeOverlayController's is being used by designers for verification.

To make that easier, the dumpsys now includes HCT coordinates, hex codes
w/o alpha channel, and the seed color, which ColorScheme now stores in
an instance variable.

Test: adb shell dumpsys activity
service com.android.systemui/.SystemUIService ThemeOverlayController;
verify format works as intended. Shared with design, got feedback and
confirmation this includes all needed info.
Change-Id: I058d390b109a27e2277a2a74c1519c7b15a49400