Use eslint-plugin-escompat in typescript config

[bdragon]

Since upgrading to eslint-plugin-github@4.4.0, linting with the plugin:github/typescript config produces tons of errors indicating that definitions for the eslint-plugin-escompat plugin can't be found:

1:1   error  Definition for rule 'escompat/no-optional-chaining' was not found                                        escompat/no-optional-chaining
1:1   error  Definition for rule 'escompat/no-nullish-coalescing' was not found                                       escompat/no-nullish-coalescing
...

If I modify my downstream project's eslintrc to include plugins: [..., 'escompat', ...] and lint again, the errors go away. I think the issue is that eslint-plugin-escompat is a dependency of the typescript config for estlint-plugin-github but is not included in the config, so the downstream project fails trying to find it. I'm hoping this change will fix it.