☔ Migration to `package:unified_analytics` for analytics collection

[eliasyishak]

This serves as a tracker issue for the migration efforts for devtools to package:unified_analytics

Tasks:

• Setup the analytics instance and integrate the necessary APIs for onboarding a new user
  • PR in flutter/devtools to add logic: Setting up package:unified_analytics within devtools #7084
  • PR in dart-lang/tools to check legacy file: Checking for devtools config file for opt out dart-lang/tools#227
  • PR in dart-lang/tools to fix behavior for showing message: Fix logic for first run to fix shouldShowMessage behavior dart-lang/tools#228
  • [SWAP WITH PR] Have IDEs that start DTD pass their identifier #7230 tracked separately in Have IDEs that start DTD pass their identifier #7230

Migration for events

• Select (selecting tabs)
  • PR in dart-lang/tools to add event: Event Constructor added for devtools event dart-lang/tools#258
  • PR in flutter/devtools to use event: Migrate select event to package:unified_analytics #7479
• Timing events (Send timing, screen, impression, and exception events through unified_analytics #7676)
• Screen views (Send timing, screen, impression, and exception events through unified_analytics #7676)
• Impressions (Send timing, screen, impression, and exception events through unified_analytics #7676)
• Exceptions (Send timing, screen, impression, and exception events through unified_analytics #7676)