Consider exposing more functionality in `devtools_app_shared`

[kenzieschmoll]

Some suggestions based on the creation of shared_preferences_tool: flutter/packages#6749

• DevToolsClearableTextField: https://github.com/flutter/devtools/blob/master/packages/devtools_app/lib/src/shared/common_widgets.dart#L839
  • done in Move some common widgets and utilities to devtools_app_shared #7979
• RoundedDropdownButton: https://github.com/flutter/devtools/blob/master/packages/devtools_app/lib/src/shared/common_widgets.dart#L755
  • done in Move some common widgets and utilities to devtools_app_shared #7979
• search and filter UI elements
• utilities like caseInsensitiveFuzzyMatch: https://github.com/flutter/devtools/blob/master/packages/devtools_app/lib/src/shared/primitives/utils.dart/#L959
  • done in Move some common widgets and utilities to devtools_app_shared #7979