Include module file and context dependencies in ConcatenatedModule

As ModuleConcatenationPlugin removes the concatenated modules from a
compilation, the file and context dependencies of those modules needs
to be stored in the ConcatenatedModule for webpack to be able to watch
those paths.

lib/optimize/ConcatenatedModule.js

@@ -154,6 +154,8 @@ class ConcatenatedModule extends Module {
 		this.dependencies = [];
 		this.dependenciesWarnings = [];
 		this.dependenciesErrors = [];
+		this.fileDependencies = [];
+		this.contextDependencies = [];
 		this.warnings = [];
 		this.errors = [];
 		for(const m of modules) {
@@ -164,6 +166,10 @@ class ConcatenatedModule extends Module {
 			m.dependenciesWarnings.forEach(depWarning => this.dependenciesWarnings.push(depWarning));
 			// populate dep errors
 			m.dependenciesErrors.forEach(depError => this.dependenciesErrors.push(depError));
+			// populate file dependencies
+			if(m.fileDependencies) m.fileDependencies.forEach(file => this.fileDependencies.push(file));
+			// populate context dependencies
+			if(m.contextDependencies) m.contextDependencies.forEach(context => this.contextDependencies.push(context));
 			// populate warnings
 			m.warnings.forEach(warning => this.warnings.push(warning));
 			// populate errors