fix(material/tabs): tabgroup update selectedIndex

[markusingvarsson]

trafficstars

Fixes an issue with the tab group where the selectedIndex was not properly maintained when the number of tabs changed.

Fixes #26816

[allexgut]

@markusingvarsson Are you planning on fixing the integration tests here? If not, I can take over your changes and try to fix the integration tests so this could be ready for merging.

[parijat93sharma]

i think this is already fixed and merged https://github.com/angular/components/pull/28256

[andrewseguin]

Indeed this seems to be resolved - I couldnt reproduce

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