"merge params" option

[blazmrak]

Added "merge params" option to application as discussed in #5006.

Note: I am not familiar with the suite, so I copy pasted mergeParams tests and adapted them a bit to the application where needed, but I just wanted to make sure that the behavior of the application is the same as the router. The tests should look the same for both however... Would it make sense to provide [Router({mergerParams: true}), app.handle] and run the same tests for them, or is it preferable to have these duplicated?

[dougwilson]

The tests should look the same for both however... Would it make sense to provide [Router({mergerParams: true}), app.handle] and run the same tests for them, or is it preferable to have these duplicated?

It's perfectly fine how you have it and we typically keep them duplicated, as we ended up having lots of accidental regressions in the past when trying to be clever in the test suite and consolidate them with various logic. I think there are still a couple places left like that.