improve how we calculate when to summarize flutter errors

[devoncarew]

• improve how we calculate when to summarize flutter errors
• fix Structure error missing parts when displayed in IntelliJ #4363

Instead of deciding to summarize errors subsequent to the first error after a reload, we instead summarize errors subsequent to the first error after a frame event. Those errors are more likely to be errors (overflow, ...) triggered by the first error.

From the flutter error sample app, navigating to the material error, then the overflow error, you can see now that the overflow triggered by the material error is summarized, but the later overflow from the overflow page is not.

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[stevemessick]

Good idea!