Flutter Deprecations (Part 2)

[parthshindee]

Time Tracking: MA-95

This is done when:

• [x] Resolve 'caption' is deprecated and shouldn't be used
• [x] Resolve Name non-constant identifiers using lowerCamelCase
• [x] Resolve Unnecessary import
• [x] Resolve Value isn't used
• [x] Resolve The '!' will have no effect because the receiver can't be null
• [x] Resolve 'backgroundColor' is deprecated and shouldn't be used

Test Plan

• [ ] PR 2054 Test Plan PASS on iOS
• [ ] PR 2054 Test Plan PASS on Android

[morebytes]

As part of Dart 3 migration, I ended up working around it in a different way and discovered new issues. Let's discuss after it goes through...