[ios] `HybridGlobalization`, functions calculating `matchLength` should return PNSE

[ilonatommy]

Follow up PR for iOS based on changes in #105946.

• IndexOf/LastIndexOf should throw PNSE
• block tests that throw because of that
• re-check that docs about it are up to date

[dotnet-policy-service]

Tagging subscribers to 'arch-wasm': @lewing
See info in area-owners.md if you want to be subscribed.

[dotnet-policy-service]

Tagging subscribers to 'os-ios': @vitek-karas, @kotlarmilos, @ivanpovazan, @steveisok, @akoeplinger
See info in area-owners.md if you want to be subscribed.

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/area-system-globalization
See info in area-owners.md if you want to be subscribed.

[vitek-karas]

@matouskozak