Issue #1392754 by tss, justAChris, jhodgdon: Comply with new documentation standards for @file for namespaced class files

Issue #2342551 by larowlan: Implement ThirdPartySettingsInterface in contact module for contact form config entity.

Issue #2030591 by jibran, Temoor, andypost, lokeoke, er.pushpinderrana, martin107, pcambra, piyuesh23, Sharique, kgoel | plopesc: Expand ContactForm with methods.