Make all properties in TreeshakingOptions optional

[ndelangen]

This is what the docs are telling me the types should be: https://rollupjs.org/guide/en#treeshake

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes
• no

Breaking Changes?

• yes
• no

Description

I was using the Node API in typescript and typescript was telling me:

Type '{ pureExternalModules: boolean; }' is not assignable to type 'boolean | TreeshakingOptions'.
  Type '{ pureExternalModules: boolean; }' is missing the following properties from type 'TreeshakingOptions': annotations, propertyReadSideEffectsts(2322)
rollup.d.ts(286, 2): The expected type comes from property 'treeshake' which is declared here on type 'RollupOptions'

I was able to fix the warning by adding all 3 properties to the TreeshakingOptions.

Looking at the docs, I concluded that the interface is actually wrong.

I'm unsure this qualifies as a bugfix.

[ndelangen]

Have an awesome day people, this package is awesome!

[lukastaegert]

Looks good, thanks a lot! Small fixes like this are always very welcome!