[core] Add exports field and build proper ES modules

[michaldudak]

Builds "true" ES modules alongside CommonJS output.

Summary of changes

• ESM build output is placed under /build/esm
• CommonJS build output is placed under /build/cjs
• Per-component package.json files were removed
• The exports field was added to the package
• The typesVersion field was added to package.json for compatibility with older tsconfig settings
• Type definitions are built per target - the CJS one with module: "nodenext", the other one with module: "esnext".
• Are The Types Wrong CLI is executed on CI to check if no issues with the package are introduced.

Type definitions

To verify if different methods of module resolution in TypeScript can resolve the exported types, the Are The Types Wrong (ATTW) tool was used. Its reports led to building the type definitions per build output (to avoid errors like False CJS and False ESM.
Another reported issue was the inability to resolve types under the node10 module resolution when the exports field is used. While we don't support Node 10, Typescript uses this resolution strategy by default (see https://github.com/arethetypeswrong/arethetypeswrong.github.io/blob/main/docs/problems/NoResolution.md#false-positive-unsupported-file-extension).
To work around this, I introduced the typesVersions field in package.json, as described in https://github.com/andrewbranch/example-subpath-exports-ts-compat/tree/main/examples/node_modules/types-versions-wildcards.

Testing

I created a repo to test the package with different bundlers and plain Node.js: https://github.com/michaldudak/base-ui-bundler-tests. There is an issue with running a Node.js app in ESM mode due to Base UI dependency on @mui/utils. The utils package does not currently conform to the ESM spec and cannot be used without a bundler this way.
As we're planning to move away from it and define our utilities locally, this won't be a problem for long.

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This is built on top of #812

[mui-bot]

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[michaldudak]

Superseded by #821