Add codemod for border style compatibility (#14746)

This PR adds a codemod that ensures that the border styles from Tailwind CSS v3 work as expected once your project is migrated to Tailwind CSS v4.

In Tailwind CSS v3, the default border color is `colors.gray.200` and in Tailwind CSS v4 the default border color is `currentColor`.

Similarly in Tailwind CSS v3, DOM elements such as `input`, `select`, and `textarea` have a border width of `0px`, in Tailwind CSS v4, we don't change the border width of these elements and keep them as `1px`.

If your project happens to already use the same value for the default border color (`currentColor`) as we use in Tailwind CSS v4, then nothing happens. But this is very unlikely, so we will make sure that we honor your `borderColor.DEFAULT` value.

If you didn't change the default values in your `tailwind.config.js`, then we will inject compatibility CSS using the default Tailwind CSS v3 values to ensure the default color and width are applied correctly.

Author: RobinMalfait

CHANGELOG.md

@@ -14,6 +14,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - _Upgrade (experimental)_: Migrate `max-w-screen-*` utilities to `max-w-[var(…)]`([#14754](https://github.com/tailwindlabs/tailwindcss/pull/14754))
 - _Upgrade (experimental)_: Migrate `@variants` and `@responsive` directives ([#14748](https://github.com/tailwindlabs/tailwindcss/pull/14748))
 - _Upgrade (experimental)_: Migrate `@screen` directive ([#14749](https://github.com/tailwindlabs/tailwindcss/pull/14749))
+- _Upgrade (experimental)_: Generate compatibility styles for legacy default border color ([#14746](https://github.com/tailwindlabs/tailwindcss/pull/14746))
+- _Upgrade (experimental)_: Generate compatibility styles for legacy default border width on form elements ([#14746](https://github.com/tailwindlabs/tailwindcss/pull/14746))
 
 ### Fixed