[Copilot]

Adds a new MSBuild property to suppress emission of the IgnoresAccessChecksToAttribute class definition — useful when the attribute is already declared elsewhere (e.g. by another package) and you'd otherwise get a duplicate type error.

Usage

<PropertyGroup>
  <IgnoresAccessChecksToOmitAttributeDefinition>true</IgnoresAccessChecksToOmitAttributeDefinition>
</PropertyGroup>

When set, the generated file still contains the [assembly: ...] attribute usages but omits the class definition.

Changes

• PublicizeInternals.cs — adds OmitAttributeDefinition bool task property; extracts content generation into internal static BuildAttributeFileContent() which conditionally omits the class definition
• IgnoresAccessChecksToGenerator.targets — wires $(IgnoresAccessChecksToOmitAttributeDefinition) → OmitAttributeDefinition on the task invocation
• test/IgnoresAccessChecksToGenerator.Tasks.Test/ — new xUnit project with 4 tests covering default and omit behaviors for single and multiple assembly names
• README.md — documents the new property with an example