ProjectExplorer: Generalize the concept of custom output parsers

They can now be created independently of any toolchains, and we expose
them in the build and run configurations, so that users can easily get
tasks for output that comes from custom tools or is otherwise specific
to the user's environment.

Fixes: QTCREATORBUG-23993
Change-Id: I405753b9b68508ffe5deb4fcac08d6b213c7554d
Reviewed-by: André Hartmann <aha_1980@gmx.de>
Reviewed-by: hjk <hjk@qt.io>

src/plugins/projectexplorer/buildconfiguration.h

@@ -79,6 +79,9 @@ public:
 
     virtual void addToEnvironment(Utils::Environment &env) const;
 
+    const QList<Core::Id> customParsers() const;
+    void setCustomParsers(const QList<Core::Id> &parsers);
+
     BuildStepList *buildSteps() const;
     BuildStepList *cleanSteps() const;