Nim: Move a few factories to their product's compilation units

There's several hundred kBytes extra for the separate .o in a
debug build, this doesn't scale well for a handful lines of code.

As the Nim plugin is a nice template for others elsewise, it would
be nice to use scalable patterns only.

Change-Id: I78e473d28a6a63d458dcbe06a77d93221867417f
Reviewed-by: Filippo Cucchetto <filippocucchetto@gmail.com>
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/nim/project/nimcompilerbuildstep.cpp

@@ -285,6 +285,17 @@ void NimCompilerBuildStep::updateTargetNimFile()
         setTargetNimFile(nimFiles.at(0));
 }
 
+// NimCompilerBuildStepFactory
+
+NimCompilerBuildStepFactory::NimCompilerBuildStepFactory()
+{
+    registerStep<NimCompilerBuildStep>(Constants::C_NIMCOMPILERBUILDSTEP_ID);
+    setDisplayName(tr("Nim Compiler Build Step"));
+    setSupportedStepList(ProjectExplorer::Constants::BUILDSTEPS_BUILD);
+    setSupportedConfiguration(Constants::C_NIMBUILDCONFIGURATION_ID);
+    setRepeatable(false);
+}
+
 } // namespace Nim
 
 #ifdef WITH_TESTS