Increase DX by providing pre-configured transformers

[nvh95]

What & Why

• Currently, we are providing users process functions such as processFile, processFileCRA, processCss, then, they can implement the code transform by themselves. We gave users the flexibility to customize their own transformer.
• However, most of the time, users don't want to deal with the complexity of configuring transformers by themselves. That's not a great DX looks like.
• Applying the rule Don't make me think, we should provide them a just work/an opinioned solution. Then, integrating jest-preview will be very easy.

How

• Build pre-configured transformers then bundle them when building. Then, users can use that without configuring by themselves (of course they can still customize it if they want by using exported process functions)
• The code looks similar to this:

// jest.config.js
transform: {
  '^.+\\.css$': 'jest-preview/cssTransform.js',
  '^(?!.*\\.(js|jsx|mjs|cjs|ts|tsx|css|json)$)': 'jest-preview/fileTransform.js',
},

• We might need to update the docs to encourage users to use pre-configured transformers instead of using process functions (< 0.2.0)
  • The docs is getting complex and complex over time. So the need for a documentation website is getting real Need a docs site (with full text search ability) #35

When

• This is not a brand new feature. Just a wrapper for an existing one. So it's basically an improvement, does not introduce any breaking changes. So releasing it in a patch version is OK.