Reduce the complexity of dotnet tools by reducing the use of asset files

[JL03-Yue]

Given the install method of .net tools is updated from restoring template project to downloading tools from NuGet in #33835 ,per comment and comment, we might consider reduce the use of getting information from asset files to reduce complexity and improve runtime performance

If DotnetToolSettings.xml file is mostly used, using Directory.EnumerateFiles could reduce a lot of complexity and improve runtime performance than create asset files by using DotnetToolSettings.xml as the search pattern, then using a regex to figure out all TFMs and RIDs, then finally use NuGet's APIs only to select the best/closest TFM and RID.

Per [comment] (#33835 (comment)) and comment, There are multiple parts to signature verification. For NuGet, NuGet has commands dotnet nuget trust for managing the nuget trust store. Further discussion might be needed for signature verification.

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[baronfel]

We support this now via RID-specific tools as of .NET 10 preview 6.