Preselections: consider all Representations for Capability checks

[stschr]

This is a follow up on #4790
As discussed during the F2F meeting 2025-06-23, we want to check support for all Representations in the main AdaptationSet of a Preselection.

see src/dash/models/DashManifestModel.js: getCommonRepresentationForPreselection()

Note that this issue is only relevant when Preselection@codecsis different to AdaptationSet@codecs for the respective "Main Adaptation Set".