Add separateDataFiles to @rnw/cli and @rnw/codegen

[ZihanChen-MSFT]

Description

Type of Change

• New feature (non-breaking change which adds functionality)

Why

In devmain there are already requirements that, types involved in a turbo module needs to be part of the API.
Such project structure would be:

• The API implemented in C++
• Native code calls the API
• The turbo module calls the API
• JS code calls the turbo module

When a feature needs to be available to both C++ and JS, it is possible that the API and the turbo module will share some data structures. If by semantic they are always exactly the same, why not just publish generated types?

What

In order to complete the story, the turbo module C++ codegen needs to generate a clean header files for custom types if required. Setting codegenConfig.windows.separateDataTypes does this.

Testing

Tested in sample-apps

Changelog

Should this change be included in the release notes: yes

npx react-native codegen-windows will generate two files if there is any custom type to generate. The additional file NativeXXXDataTypes.g.h contains all generated custom types.

Microsoft Reviewers: codeflow:open?pullrequest=https://github.com/microsoft/react-native-windows/pull/11990&drop=dogfoodAlpha

[acoates-ms]

Can we split the two files into separate generators, which would align with core where there are separate generators for the cpp vs h files?
Then instead of having to have another option for the config, we can just specify the generators we require.

[ZihanChen-MSFT]

Can we split the two files into separate generators, which would align with core where there are separate generators for the cpp vs h files? Then instead of having to have another option for the config, we can just specify the generators we require.

Both file needs the input (in the intermediate format) to be compiled again to identify anonymous custom types before generating it, they shared many complex logic. I think it is good to just keep them in one generator.

[vmoroz]