[GB18030] Audit shipped props and targets for usage of Substring on paths

[JanKrivanek]

Context

Based on issue identified by @ilonatommy and @ladipro (https://github.com/dotnet/msbuild/pull/10063) Substring doesn't resect surrogate chars

Sample GH query (though needs to be tunned up, or just search locally): https://github.com/search?q=Substring+repo%3Adotnet%2Fmsbuild+path%3A**%2F*.targets&type=code&ref=advsearch

[JanKrivanek]

In msbuild we have just the single usage being fixed.

There are couple similar usages in Blazor targets in sdk: https://github.com/search?q=repo%3Adotnet%2Fsdk+path%3A**%2F*.targets+substring&type=code

Once the fix is inserted we should reach out to them or shoot a PR

[JanKrivanek]

Handled in scope of https://devdiv.visualstudio.com/DefaultCollection/DevDiv/_workitems/edit/2031987/?view=edit