Rework TypeScript .d.ts handling

This reworks .d.ts handling to address the issues in #977 and reported by [Are the Types Wrong](https://arethetypeswrong.github.io/?p=chartjs-plugin-annotation%403.1.0).

Background information:

* According to the [TypeScript Handbook](https://www.typescriptlang.org/docs/handbook/modules/guides/choosing-compiler-options.html#im-writing-a-library):

    > If you’re using a bundler to emit your library... You must ensure that your declaration files get bundled as well. Recall the [first rule of declaration files](https://www.typescriptlang.org/docs/handbook/modules/theory.html#the-role-of-declaration-files): every declaration file represents exactly one JavaScript file.

* According to [Are the Types Wrong](https://github.com/arethetypeswrong/arethetypeswrong.github.io/blob/main/docs/problems/FalseESM.md),

    > A golden rule of declaration files is that if they represent a module—that is, if they use import or export at the top level—they must represent exactly one JavaScript file. They especially cannot represent JavaScript files of two different module formats.

* chartjs-plugin-annotation's CJS build uses a CJS default export (see [Rollup's docs](https://rollupjs.org/configuration-options/#output-exports)). Properly representing that in a `.d.ts` file requires using `export = Annotation`, but the `export =` syntax both raises challenges for exporting types alongside the default export and is incompatible with ESM. (The [TypeScript Handbook](https://www.typescriptlang.org/docs/handbook/modules/appendices/esm-cjs-interop.html) has even more background information here. See also [tshy's documentation](https://github.com/isaacs/tshy?tab=readme-ov-file#handling-default-exports), "`export default`` is the bane of hybrid TypeScript modules" - although I believe that the situation is [not quite as bad as it says](isaacs/tshy#105).)

Pulling this together for chartjs-plugin-annotation:

* Use [rollup-plugin-dts](https://www.npmjs.com/package/rollup-plugin-dts) to bundle declaration files alongside the bundled library files (as recommended by the TypeScript Handbook).
* Invoke rollup-plugin-dts twice to create separate `.d.ts` files for the ESM and CJS builds (and update package.json to reference those).
* Although a CJS file with a default export can't export additional values, it is apparently possible to export types alongside the default value, if the types are placed in a namespace with the same name as the default value.
* I had trouble finding a solution for the `export =` default issue. (I couldn't get rollup-plugin-dts to create an `export =` style definition. Changing chartjs-plugin-annotation to not use a CJS default export may be the simplest long-term solution, but it would break backward compatibility.) To solve this, I added @rollup/plugin-replace to apply the necessary namespace and `export =` statement via string replacement.

Fixes #977

Author: joshkel