fix: stop using filter in module generation schematic

[sis0k0]

Let's say that you execute the command:

ng g migrate-module about

Before this PR:

• The migrate-module schematic uses the module schematic to generate a NgModule with name='about';
• the module schematic filters out the files that end with about.module.ts - this is done because otherwise the we'll get a merge conflict;
• the module schematic uses the external @schematics/angular module schematic to generate about.module.ts;
• the migrate-module schematic renames about.module.ts to about.module.tns.ts.

Unfortunately, the filter function visits all files in node_modules and platforms and slows down the execution of the module schematic significantly.

With this PR:

• The migrate-module schematic generates a NgModule file from a template instead of relying on the module schematic.
• The module schematic doesn't use filter anymore, which speeds up the execution of the command.

fixes #185, #203

[KristianDD]

Do we import this just to load the Schema? I am asking as it seems that the next line will override the Schema value.

[sis0k0]

Schema refers to the name of the export imported from the '../common-module/schema' module, whereas CommonModuleSchema refers to the binding imported into the local module scope. In short: CommonModuleSchema and ModuleOptions (next line) will be the local names of the imported symbols.