[Minor] Refactor MSBuild project structure

[Belonit]

Refactors the MSBuild project layout and prepares the build configuration for safer optimized builds.

Changes:

• Split Phobos build settings into Phobos.props.
• Import project-wide props from Phobos.vcxproj.
• Cleaned up duplicated and redundant MSBuild settings.
• Prepared linker retention settings for WPO/LTCG compatibility.

[github-actions]

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