utils: Add multi video and frame rate divisor support to GetOutputDuration

[exeldro]

Description

Add multi video and frame rate divisor support to Utils::Obs::NumberHelper::GetOutputDuration

Motivation and Context

Fixes #1273

How Has This Been Tested?

With outputs with multiple video tracks of which some have frame rate divisors Tested OS(s): Windows 11

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• [x] I have read the Contributing Guidelines.
• [x] All commit messages are properly formatted and commits squashed where appropriate.
• [x] My code is not on master or a release/* branch.
• [x] The code has been tested.
• [x] I have included updates to all appropriate documentation.

[tt2468]

The correct prefix for this commit would be utils:, rather than base.