fix(types): Support undefined in NavigationGuardNext

[Thomasan1999]

Add support for undefined as the first argument in next function in navigation guards. I've decided to do it through making location argument optional since it seems to me as using undefined is omitting redefining the next route location.

Related to: #1058

[posva]

Let's add it to the Boolean argument instead as an explicit undefined. Can you also add a test in the dts tests?

[posva]

Thanks!