GraphQL Typegen should write gatsby-types.d.ts only when it is changed

[kota65535]

This Ideas / Feature Request originated from #37983 and #38045.

I want to perform TypeScript type-checking on every Fast Refresh.
This can be done by adding a custom configuration of fork-ts-checker-webpack-plugin in onCreateWebpackConfig.

But when I enabled GraphQL Typegen with this configuration, I'm stuck in an infinite loop of Fast Refresh.
This is because fork-ts-checker-webpack-plugin adds gatsby-types.d.ts to compilation.fileDependencies, whose changes are watched by webpack.

1. Dev server begins to watch gatsby-types.d.ts
2. I change any file
3. Fast refresh runs and gatsby-types.d.ts is re-created
4. Because gatsby-types.d.ts is changed, Fast Refresh runs and then gatsby-types.d.ts is re-created
5. Because gatsby-types.d.ts is changed, Fast Refresh runs and then gatsby-types.d.ts is re-created
6. ...

I think the simple solution to this problem is to write gatsby-types.d.ts only when the file is changed.

gatsby/packages/gatsby/src/utils/graphql-typegen/ts-codegen.ts

Line 163 in 8c9b0d4

await fs.outputFile(filename, result)

The code change can be as follows:

  if (await fs.pathExists(filename) && result === await fs.readFile(filename, 'utf8')) {
    return;
  }
  await fs.outputFile(filename, result);

I would like to make a PR if this idea is OK.