msgs: more decision making in handleReport

[zerbina]

Summary

• fix hints/warnings promoted to errors always counting towards the
  maximum error count, even if the hint/warning is currently disabled
• fix disabled warnings and hints being reported by nimsuggest chk

Details

Processing of a Report previously worked as follows:

1. handleReport pre-processes the report
2. the report is passed to the report hook
3. the hook outputs the report if it determines that the report should
   be rendered and displayed
4. handleReport determines the error handling strategy
5. error handling is performed

This has two problems:

1. the responsibility of deciding whether a report should be output is
   left to the hook, which also means that the hook needs access to all
   state necessary to make the decision
2. error handling always takes place, even if the report is disabled

Report handling is split up, and the responsibilities are shifted:

1. if a report is disabled (isEnabled returns false), handleReport
   is a no-op
2. deciding writability is now the responsibility of handleReport
   (i.e., the compiler), with the report hook only invoked if the
   report is eligible for being displayed
3. computing writability no longer takes into account whether the
   report is enabled (since writeability is only decided after it is
   known that a report is enabled)
4. handleReport now handles the "forcefully enabled" case, by
   temporarily overriding the writeln hook with something that always
   echoes the message (this mirrors the previous behaviour of the
   report hook implementations)

In short, more responsibility regarding reports shift into a single
place (handleReport), with the report hook now only being invoked for
reports that should be displayed. Centralizing Report handling is a
step towards eventually removing/replacing Reports.

Since the the report hook used by nimsuggest doesn't consider
writeability ( writabilityKind ), this fixes all produced warnings
being
reported by chk, even those that are disabled.

Finally, disabled reports no longer triggering error handling fixes
disabled warnings promoted to errors being able to abort compilation.

[saem]

Nice fix, and also glad it cuts away more of the report hook mess.

[saem]

/merge

[github-actions]

Merge requested by: @saem

Contents after the first section break of the PR description has been removed and preserved below:

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Notes for Reviewers

• discovered while trying to enable --warningAsError:UnusedImport for the CI
• this seems to be a regression from Structured reports #94