DevTools 2.40.2 cherrypick release

[kenzieschmoll]

Rationale for cherry pick:

1. There are a couple of issues with our analytics that will prevent us from being able to properly monitor the rollout of the Dart2wasm and Flutter Inspector V2 experiments.

• 77eae8f6c8382ef042120a20db3d34e1c3cce7af (a pre-requisite to avoid merge conflicts for the following two changes)
• Include stack traces with unified_analytics exception events. #8510
• Include screen information with unified_analytics events and bump unified_analytics to 7.0.0 #8514

3. There are a couple of issues with the Inspector V2 code that we should include in the cherry pick to make the new experience more robust / polished before rolling out to users.

• [Inspector V2] Fixes an issue where the V2 Inspector wouldn't load after hot-restarting from legacy inspector  #8491
• [Inspector V2] Handle selection of an implementation widget in the app #8494
• Alternating colors look nice in tables when embedded in IDE #8498

This DevTools CP release into the Dart SDK beta branch will need to be accompanied by another cherry-picked commit into the Dart SDK:
- [ ] https://dart-review.googlesource.com/c/sdk/+/394006, which bumps the unified_analytics version used in the SDK to ^7.0.0.

• https://dart-review.googlesource.com/c/sdk/+/397001, which bumps the unified_analytics version used in the SDK to 7.0.1