Move .editorconfig and update ProjectDefaults version

Relocated .editorconfig from src/ to the repository root and updated its reference in DiffEngine.slnx. Also bumped ProjectDefaults package version from 1.0.168 to 1.0.170 in Directory.Packages.props.

Author: SimonCropp

src/.editorconfig .editorconfigsrc/.editorconfig renamed to .editorconfig

@@ -8,7 +8,7 @@
     <File Path="../appveyor.yml" />
     <File Path="../claude.md" />
     <File Path="../readme.source.md" />
-    <File Path=".editorconfig" />
+    <File Path="../.editorconfig" />
     <File Path="Directory.Build.props" />
     <File Path="Directory.Packages.props" />
     <File Path="global.json" />

src/DiffEngine.slnx

@@ -12,7 +12,7 @@
     <PackageVersion Include="Microsoft.Sbom.Targets" Version="4.1.5" />
     <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.0.1" />
     <PackageVersion Include="Polyfill" Version="9.4.1" />
-    <PackageVersion Include="ProjectDefaults" Version="1.0.168" />
+    <PackageVersion Include="ProjectDefaults" Version="1.0.170" />
     <PackageVersion Include="Resourcer.Fody" Version="1.8.1" />
     <PackageVersion Include="Serilog" Version="4.3.0" />
     <PackageVersion Include="Serilog.Sinks.File" Version="7.0.0" />