unify(shell): Move Shell to Core

[Jaredl-Dev]

This merges the shared Shell implementation and moves it into Core:

• Shell.h
• Shell.cpp
• ShellHooks.h
• ShellMenuScheme.h
• ShellMenuScheme.cpp

Before this change, Generals and Zero Hour differed only by product-name comments and the RTS_PROFILE_LEGACY initialization profiling hook in Shell.cpp.

Generals gets

• Stops the legacy init profiling range before opening the main menu, matching Zero Hour.

Dependency cleanup

Because profile builds of the shared Shell call Profile::StopRange("init"):

• Both GameEngine builds inherit core_profile_legacy through corei_gameengine_private.
• core_profile_legacy privately links core_debug.
• Redundant direct profiler and debug links were removed from the Generals and Zero Hour executables and tools.

Verification

• Verified all four Core files match the former Zero Hour sources.
• Win32 Release build succeeds.
• VC6 Release build succeeds.
• Win32 Profile and VC6 Profile builds succeed at both commits.

[Jaredl-Dev]

Generals now inherits Profile::StopRange("init"), but unlike Zero Hour, it never calls StartRange("init"). Should it be added to Generals’ WinMain.cpp?

[Jaredl-Dev]

I've revised this PR and updated the body to reflect the changes. Please also review my question above.