[flutter_tools] Fix missing stack trace from daemon

[jiahaog]

When the daemon throws an exception, the receiving client is unable to surface stack traces from the daemon.

This is because it is sent with the trace key here:

flutter/packages/flutter_tools/lib/src/daemon.dart

Line 308 in 1e8dd1e

'trace': '$trace',

But the client tries to read it with the stackTrace key here:

flutter/packages/flutter_tools/lib/src/daemon.dart

Line 343 in 1e8dd1e

final String stackTrace = data['stackTrace'] as String? ?? '';

Thanks to @mraleph for spotting this!

List which issues are fixed by this PR. You must list at least one issue. An issue is not required if the PR fixes something trivial like a typo.

b/326825892

Pre-launch Checklist

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• I read the [Tree Hygiene] wiki page, which explains my responsibilities.
• I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement].
• I signed the [CLA].
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is [test-exempt].
• I followed the [breaking change policy] and added [Data Driven Fixes] where supported.
• All existing and new tests are passing.

[jiahaog]

Overwrote the Google Testing status because the failing test was already failing and unrelated to this PR.

[chingjun]

Thanks for spotting this!