[rc2] Remove EFOptimizeContext property from EF targets

[Copilot]

This change removes the EFOptimizeContext MSBuild property from Entity Framework Core's build targets, as the existing EFScaffoldModelStage and EFPrecompileQueriesStage properties provide sufficient control over code generation.

Changes Made

Microsoft.EntityFrameworkCore.Tasks.targets:

• Removed EFOptimizeContext conditions from _EFGenerateFilesAfterBuild and _EFGenerateFilesBeforePublish targets
• Updated documentation comments to reflect that stage properties are the primary control mechanism

PACKAGE.md:

• Updated usage instructions to focus on stage properties instead of EFOptimizeContext
• Provided clearer guidance on controlling when code generation occurs

RootCommand.cs:

• Modified dotnet ef dbcontext optimize command to disable generation using stage properties (/p:EFScaffoldModelStage=none /p:EFPrecompileQueriesStage=none) instead of /p:EFOptimizeContext=false

Impact

This is a simplification that removes a redundant control mechanism. Users can still control when Entity Framework code optimization occurs, but now exclusively through the more granular stage properties:

• EFScaffoldModelStage=build|publish|none - Controls compiled model generation
• EFPrecompileQueriesStage=build|publish|none - Controls precompiled query generation

The default behavior remains unchanged - both features are enabled for the publish stage by default.

Fixes #35079.

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