fix: Eliminate TS2312 error in router.d.ts

[octogonz]

This is a fix for #129 and #94

If we wanted to be more correct but less ergonomic, an alternate possibility would be:

// A simplified version of RoutableProps that can be used with "extends"
interface JsxRoutableProps {
	path?: string;
	default?:boolean
}	

declare module 'preact' {
	namespace JSX {
		interface IntrinsicAttributes extends JsxRoutableProps {}
	}
	interface Attributes extends JsxRoutableProps {}
}

@rschristian @aymericzip

[rschristian]

Cheers

[octogonz]

I added some test cases to my repro branch:

https://github.com/octogonz/preact-iso-repro/blob/main/src/test.tsx

...and confirmed that the outcome of the test cases is unaffected by these changes.