feat: add transform-imports plugin

[sapphi-red]

This PR adds @rolldown/plugin-transform-imports which utilizes Rolldown's native magic string feature.

In the synthetic benchmark included in this PR, this plugin is

• 1.36x faster than using @swc/plugin-transform-imports + @rollup/plugin-swc
• 2.91x faster than using babel-plugin-transform-imports + @rolldown/plugin-babel

The implementation is based on swc-project/plugins/packages/transform-imports (Apache License 2.0) and test cases are also adapted from it.

Normally, the lazy barrel feature in Rolldown (currently experimental) resolves the performance problem. But in some edge cases, this plugin can improve the performance further by ignoring minor semantics.

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commit: 5c945d9

[shulaoda]

I prefer the following form:

transformImports({
  'mock-lib': {
    transform: 'mock-lib/{{kebabCase member}}',
  },
});

rather than:

transformImports({
  modules: {
    'mock-lib': {
      transform: 'mock-lib/{{kebabCase member}}',
    },
  },
});

First, the modules field feels redundant and unnecessary. Second, the former aligns better with the configuration style used by the corresponding plugins in Babel and SWC.

[shulaoda]

I pushed a small change. If you think it’s not appropriate, we can revert it at any time.

[sapphi-red]

It was to allow adding options in the future, but I guess it's ok to remove it.

[shulaoda]

It was to allow adding options in the future, but I guess it's ok to remove it.

Yes, I had the same thought about why it’s implemented that way. But after reconsidering, I think for now we should just focus on keeping things aligned. We can revisit and enhance the functionality later when there’s an actual user need.