feat: support symlinked packages

[AlCalzone]

When using package managers like pnpm or yarn v3 with the pnpm linker, the current check for methods that come from this library doesn't work. The reason is that path.resolve(signature.declaration.getSourceFile().fileName is a path like node_modules/typescript-is/index.d.ts, but path.resolve(path.join(__dirname, '..', '..', 'index.d.ts')) looks like this node_modules/.store/typescript-is-virtual-6354fcdb88/node_modules/typescript-is/index.d.ts. The former folder is a symlink to the latter.

Using fs.realpathSync we can resolve the symlinked path to the real one and make sure the transformer works in these contexts.

I threw in some caching for the lookup via PartialVisitorContext.canonicalPaths, if this isn't desired, it also works using fs directly.