Better night mode handling

Provides a default behavior for splash screen that uses light and dark
colors when available.

Test: Manual on API 27 to API 31, check that the splash screen with no
customization respect dark and light colors
Bug: 208823639
Change-Id: I60dab3006ad7e0ebd754486ec4d5a2e84d5ffee6

• core/core-splashscreen/src/main/res/values-night/styles.xml[Added - diff]
• core/core-splashscreen/src/main/res/values-v27/styles.xml[diff]
• core/core-splashscreen/src/main/res/values-v29/styles.xml[diff]
• core/core-splashscreen/src/main/res/values-v31/styles.xml[diff]
• core/core-splashscreen/src/main/res/values/styles.xml[diff]