Setting scheduler output stream count based on input

**Add a pointer to any prior users list discussion.**
https://groups.google.com/g/dynamorio-users/c/kh5LcP2uW28

**Is your feature request related to a problem? Please describe.**
I would like to set the number of output streams in the drcachesim scheduler to be equal to the number of input streams. However, the number of input streams in not known until scheduler.init has been called, but the output stream count must be passed to scheduler.init.

Similarly, when using MAP_TO_RECORDED_OUTPUT, we might want to set the number of outputs to the number of cpus in the trace.

**Describe the solution you'd like**
I would like to be able to tell the scheduler how the output count should be set instead of specifying the actual value. We'll need a way to query the output count also.

Do you have any implementation in mind for this feature?

**Describe alternatives you've considered**

**Additional context**