Improve compatibility with typescript-eslint's Config model

[JasonWeinzierl]

This fixes compatibility with the TSESLint.FlatConfig.Rules interface from @typescript-eslint/utils.

Resolves #377

Description

When using TypeScript to write an ESLint flat config, the following will cause a compile error:

// @ts-check
import tseslint from 'typescript-eslint';
import jasmine from 'eslint-plugin-jasmine';

export default tseslint.config({
  plugins: {
    jasmine,
  },
  extends: [
    jasmine.configs.recommended,
  ],
});

Type '{ rules: { 'jasmine/expect-matcher': number; 'jasmine/expect-single-argument': number; 'jasmine/named-spy': number; 'jasmine/no-focused-tests': number; 'jasmine/no-disabled-tests': number; 'jasmine/no-describe-variables': number; ... 15 more ...; 'jasmine/prefer-toBeUndefined': number; }; }' is not assignable to type 'Config'.
  Types of property 'rules' are incompatible.
    Type '{ 'jasmine/expect-matcher': number; 'jasmine/expect-single-argument': number; 'jasmine/named-spy': number; 'jasmine/no-focused-tests': number; 'jasmine/no-disabled-tests': number; 'jasmine/no-describe-variables': number; ... 15 more ...; 'jasmine/prefer-toBeUndefined': number; }' is not assignable to type 'Partial<Record<string, RuleEntry>>'.
      Property ''jasmine/expect-matcher'' is incompatible with index signature.
        Type 'number' is not assignable to type 'RuleEntry | undefined'.ts(2322)

This PR fixes this error by doing the JSDoc-equivalent of TypeScript's as const, narrowing each value of rules from number to 0|1|2.

How has this been tested?

1. Edited the index.js in node_modules.
2. The error goes away and ESLint continues to work.
3. Ran npm run test

Types of changes

• Test change (non-breaking change which adds additional test scenarios)
• Refactor change (non-breaking change updates coding styles)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I have ran npm run test and everything passes
• My code follows the code style of this project
• I have updated the documentation where necessary
• I have read the CONTRIBUTING document
• I have added tests to cover my changes
• All new and existing tests pass