Modernize .editorconfig and enforce IDE0003 in CI

[edwcry]

Description of the changes:

• Expand the stub .editorconfig into a single source of truth: universal defaults plus C#, C++, XML/MSBuild, JSON/YAML, and Markdown sections, including .NET naming rules and code-style preferences.
• Promote IDE0003 (remove unnecessary this. qualification) to warning and apply the fix across the CalculatorUITestFramework sources.
• Add build/scripts/VerifyCodeStyle.ps1, which runs dotnet format style --verify-no-changes on the SDK-style C# projects (CalculatorUITestFramework, CalculatorUITests). This surfaces IDE-prefixed Roslyn analyzers (IDE0003) that csc does not reliably emit at build time. Old-style UWP projects and native C++ test projects are excluded because the dotnet workspace loader cannot evaluate them.
• Add a Verify code style (IDE0003) job to action-ci.yml so the gate runs on every pull request.

How changes were validated:

• Ran dotnet format style locally (.NET SDK 10.0.301) to apply the IDE0003 fixes.
• Ran build/scripts/VerifyCodeStyle.ps1 locally; it passes with no violations on both allowlisted projects.
• No functional/runtime code changed; existing build, unit test, and UI test jobs are unmodified.

[edwcry]

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