Tweak warnings errors

[davidmorgan]

For #4127

Changes to make failures more prominent/actionable:

• move blocks of log output that do not contain errors before the status line; only errors go after the status line
• remove "log output for" and "on" from the block header, move the filename first so it's " ", and make the filename bold red if the block contains any error
• make the "E" prefix that indicates an error bold red

And, remove the "deleting declared outputs" warning, it's not actionable.

[github-actions]

PR Health

Changelog Entry ❗

Package	Changed Files
package:build_runner_core	build_runner_core/lib/src/generate/build_definition.dart build_runner_core/lib/src/logging/ansi_buffer.dart build_runner_core/lib/src/logging/build_log.dart build_runner_core/lib/src/logging/build_log_messages.dart

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