fix(webpack): find ExternalModuleFactoryPlugin where webpack 5.112 moved it - #11633

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• Tests for the changes are included - https://github.com/NativeScript/NativeScript/blob/master/tools/notes/WritingUnitTests.md.

What is the current behavior?

NativeScriptBuiltinModulesPlugin (#11626) loads webpack/lib/ExternalModuleFactoryPlugin. webpack 5.112 moved that file to webpack/lib/externals/, so on current webpack the config fails to load with Cannot find module 'webpack/lib/ExternalModuleFactoryPlugin'. This is the same kind of move #11547 fixed for WorkerDependency.

What is the new behavior?

The plugin loads webpack/lib/externals/ExternalModuleFactoryPlugin and falls back to the old path, matching the worker loader's approach. The class's constructor and apply(normalModuleFactory) are unchanged between 5.99 and 5.112.

Tested __tests__/plugins/NativeScriptBuiltinModulesPlugin.spec.ts (real ESM and CommonJS compiles) against:

• webpack 5.99.9 (the repo's version): passes.
• webpack 5.112.2, mapped in through a temporary jest config: passes with this change. Without it the suite fails to load.

CI only runs the repo's webpack version, so the 5.112 run was manual. The rest of the webpack suite is unchanged; its 14 failing snapshot tests also fail on main.