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/projectexplorer/toolchainsettingsaccessor.cpp

@@ -324,7 +324,7 @@ public:
     void addToEnvironment(Environment &env) const override { Q_UNUSED(env) }
     FilePath makeCommand(const Environment &) const override { return FilePath::fromString("make"); }
     FilePath compilerCommand() const override { return Utils::FilePath::fromString("/tmp/test/gcc"); }
-    IOutputParser *outputParser() const override { return nullptr; }
+    QList<IOutputParser *> outputParsers() const override { return {}; }
     std::unique_ptr<ToolChainConfigWidget> createConfigurationWidget() override { return nullptr; }
     bool operator ==(const ToolChain &other) const override {
         if (!ToolChain::operator==(other))