[DocsUI M3] Fix corners and selection state colours

Update the corner radii and the selection state colours to match the
figma spec.

See screenshots at b/381962394#comment2.

Bug: 381962394
Test: m DocumentsUIGoogle && manual inspection
Flag: com.android.documentsui.flags.use_material3
Change-Id: I90cf16fe1e96bb225b804dd66ac6ba0ccdac33bc