Add absolute path for reading file contents

[markieo1]

The config generation breaks when specifiying a rootDir that is different than ..

Example code that breaks:

import vueTsEslintConfig from '@vue/eslint-config-typescript';
vueTsEslintConfig({rootDir: 'src'}) 

Output:

node:fs:441
    return binding.readFileUtf8(path, stringToFlags(options.flag));
                   ^
Uncaught:
Error: ENOENT: no such file or directory, open 'components/Foo.vue'
    at Object.readFileSync (node:fs:441:20)

This PR changes the sync to use absolute paths. This way a different rootDir can be specified without breaking.

[haoqunjiang]

Thanks!