More fault handling cleanup

[jasonmalinowski]

Commit-by-commit recommended. For the addition of severities, they were chosen based on the rough criteria described for each option:

roslyn/src/Compilers/Core/Portable/InternalUtilities/FatalError.cs

Lines 260 to 286 in 0b5e47b

	/// <summary>
	/// The severity of the error, see the enum members for a description of when to use each. This is metadata that's included
	/// in a non-fatal fault report, which we can take advantage of on the backend to automatically triage bugs. For example,
	/// a critical severity issue we can open with a lower bug count compared to a low priority one.
	/// </summary>
	internal enum ErrorSeverity
	{
	/// <summary>
	/// Something failed, but the user is unlikely to notice. Especially useful for background things that we can silently recover
	/// from, like bugs in caching systems.
	/// </summary>
	Diagnostic,
	/// <summary>
	/// Something failed, and the user might notice, but they're still likely able to carry on. For example, if the user
	/// asked for some information from the IDE (find references, completion, etc.) and we were able to give partial results.
	/// </summary>
	General,
	/// <summary>
	/// Something failed, and the user likely noticed. For example, the user pressed a button to do an action, and
	/// we threw an exception so we completely failed to do that in an unrecoverable way. This may also be used
	/// for back-end systems where a failure is going to result in a highly broken experience, for example if parsing a file
	/// catastrophically failed.
	/// </summary>
	Critical
	}

[JoeRobich]

Did 'Change Signature' make this easy?

[jasonmalinowski]

It did! Although sometimes it did nothing at all, and my effort to debug that kept resulting in the debugger breaking. 😄

[RikkiGibson]

Could you please elaborate on how severities were chosen in general?

[jasonmalinowski]

@RikkiGibson Oh, forgot to update the PR for that. PR description updated now.

[sharwell]

ErrorSeverity.General should be the default. This coding pattern is unnecessarily burdensome.