updated import in 'generator.ts' to be properly resolvable without "allowSyntheticDefaultImports": true in 'tsconfig.json'

[sailingKieler]

added 'EventEmitter' interface to 'BaseGenerator' explicitly, as the emitter functionality is demanded by 'BaseGenerator' of '@yeoman/types'

[sailingKieler]

Dear committers,
today I ran into a TS compiling issue that is to due the 'old school' import in generated.ts.
I ran into that issue while writing/updating a (unit) test of a custom yeoman-based project stub generator.

It took my a while to identify the source of eval why Generator (BaseGenerator) of yeoman-generator is not compatible to BaseGenerator of @yeoman/types. Enabling "allowSyntheticDefaultImports" in our tsconfig.json solved it basically.

Nonetheless, I would appreciate if you guys could include this change to avoid that issue in future. Maybe there're more imports to be fixed?

The project at which I ran into the issue is Langium, my current contribution is eclipse-langium/langium#1298.

Thanks in advance! 🙏