Memory screen: improve useability and discoverability of the features.

[polina-c]

Survey: go/flutter-devtools-survey-2022

Based on Q1 2022 survey insights:

• Not clear how to use the tool - too hard to get anything useful out of it
• more docs about it how it works
• Hard to understand the results
• Difficult to decode
• Difficult to understand
• I wish it were more friendly for beginners and more resources to understand more about it
• exemplos reais
• Not very easy to understand
• I wish there was a tutorial in learning more about the page

[polina-c]

Subtasks: https://github.com/flutter/devtools/issues/4049