Support filtering in TreeView

[tznind]

Is your feature request related to a problem? Please describe.
Filtering a tree view means not just hiding/showing branches but also considering parents/children that match the filter. This makes most sense as a core library feature on the view rather than a hacky 'add on' that could be applied by the tree builder.

This will be handy for:
PowerShell/ConsoleGuiTools#179

Since v2 release seems quite far off and will likely take a while to be stable I think it makes sense for this to be in v1 and v2.

Describe the solution you'd like
Ability to add a filter to a TreeView to show only branches that match given criteria