Multi-target Microsoft.EntityFrameworkCore.Tools for net8.0, net9.0, net10.0

Add per-TFM dependency groups in the nuspec so that the appropriate
version of Microsoft.EntityFrameworkCore.Design is resolved based on
the consumer's target framework:
- net8.0 → Design >= 8.0.0
- net9.0 → Design >= 9.0.0
- net10.0 → Design >= 10.0.0

This prevents MissingMethodException when the Tools package pulls in a
Design version incompatible with the user's other EF Core packages.

Fixes #38107

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: AndriySvyryd

src/EFCore.Tools/EFCore.Tools.nuspec

@@ -4,9 +4,15 @@
   <metadata>
     $CommonMetadataElements$
     <dependencies>
-      <group targetFramework="$targetFramework$">
+      <group targetFramework="net8.0">
         <dependency id="Microsoft.EntityFrameworkCore.Design" version="8.0.0" />
       </group>
+      <group targetFramework="net9.0">
+        <dependency id="Microsoft.EntityFrameworkCore.Design" version="9.0.0" />
+      </group>
+      <group targetFramework="net10.0">
+        <dependency id="Microsoft.EntityFrameworkCore.Design" version="10.0.0" />
+      </group>
     </dependencies>
     <readme>docs\PACKAGE.md</readme>
   </metadata>