fix(typescript): allow for files to be nested within outDir

This change corrects a regression introduced by rollup#1728, preventing dual bundle configs from writing output files to directories nested within the directory defined in the tsconfig's outDir property.

Example:
```js
export default {
  input: 'src/index.ts', // Replace with the path to your entry TypeScript file
  output: [
    {
      dir: 'dist/cjs',
      format: 'cjs',
      sourcemap: true,
      preserveModules: true
    },
    {
      dir: 'dist/esm',
      format: 'esm',
      sourcemap: true,
      preserveModules: true
    }
  ],
  plugins: [
    json(),
    resolve(),
    commonjs(),
    typescript({
      tsconfig: 'tsconfig.json',
      compilerOptions: {
        /* Basic Options */
        target: 'ES5',
        module: 'ES2020',
        lib: ['ES2019', 'ES2020'],
        allowJs: true,
        checkJs: false,
        /* Strict Type-Checking Options */
        strict: true,
        /* Module Resolution Options */
        moduleResolution: 'node',
        esModuleInterop: true,
        /* Advanced Options */
        forceConsistentCasingInFileNames: true,
        skipDefaultLibCheck: true,
        skipLibCheck: true,
        outDir: path.join(__dirname, 'dist')
      }
    })
  ],
  external: deps // Add any external dependencies you don't want to bundle
};
```

packages/typescript/src/options/validate.ts

@@ -58,13 +58,16 @@ export function validatePaths(
   for (const dirProperty of DIRECTORY_PROPS) {
     if (compilerOptions[dirProperty] && outputDir) {
       // Checks if the given path lies within Rollup output dir
-      const fromRollupDirToTs = relative(outputDir, compilerOptions[dirProperty]!);
-      if (fromRollupDirToTs.startsWith('..')) {
-        if (outputOptions.dir) {
+      if (outputOptions.dir) {
+        const fromRollupDirToTs = relative(outputDir, compilerOptions[dirProperty]!);
+        if (fromRollupDirToTs.startsWith('..')) {
           context.error(
             `@rollup/plugin-typescript: Path of Typescript compiler option '${dirProperty}' must be located inside Rollup 'dir' option.`
           );
-        } else {
+        }
+      } else {
+        const fromTsDirToRollup = relative(compilerOptions[dirProperty]!, outputDir);
+        if (fromTsDirToRollup.startsWith('..')) {
           context.error(
             `@rollup/plugin-typescript: Path of Typescript compiler option '${dirProperty}' must be located inside the same directory as the Rollup 'file' option.`
           );