Output parsers: Replace the chaining approach

Use "flat" aggregation instead.
This is another step towards the formatter/parser merger.
Along the way, also fix some some subclasses (mostly in BareMetal) that
erroneously forwarded handled output to other parsers.

Task-number: QTCREATORBUG-22665
Change-Id: I12947349ca663d2e6bbfc99efd069d69e2b54969
Reviewed-by: hjk <hjk@qt.io>

src/plugins/nim/project/nimtoolchain.cpp

@@ -120,9 +120,9 @@ void NimToolChain::setCompilerCommand(const FilePath &compilerCommand)
     parseVersion(compilerCommand, m_version);
 }
 
-IOutputParser *NimToolChain::outputParser() const
+QList<IOutputParser *> NimToolChain::outputParsers() const
 {
-    return nullptr;
+    return {};
 }
 
 std::unique_ptr<ProjectExplorer::ToolChainConfigWidget> NimToolChain::createConfigurationWidget()