Referencing both Bond.CSharp and Bond.Compiler.CSharp produces "Duplicate BondCodegen items were included" error

[chwarr]

If both of the Bond.CSharp and Bond.Compiler.CSharp packages are referenced in the same SDK-style csproj file, an error about "Duplicate BondCodegen items were included" will be emitted.

This is caused by each package including Common.props and Common.targets, so the <BondCodegen Include="**/*.bond" /> item in Common.props is evaluated twice, which results in the duplicate items in BondCodegen.

Work-around: only reference Bond.CSharp xor Bond.Compiler.CSharp.

The codegen targets should detect this and emit an error. Bonus points if they handle this automatically instead.

Conditional MSBuild imports have, historically, confused Visual Studio, so an approach like <Import Project="Common.props" Condition=" '$(_bond_common_props_imported)' != 'true' " /> is probably not viable.