[Spa] Add SettingsIntro

SettingsIntro is different from SettingsBody, SettingsBody displayed
in secondary style, which SettingsIntro does not.

Also SettingsIntro's fount size is larger.

And change SettingsBody's style back to original.

Fix: 417374093
Flag: EXEMPT bug fix
Test: visual
Test: unit test
Change-Id: Ied558e4198ef5e7f40e06a2ff74beeb215e7e0da