feat(store): pass state to getters as first argument

feat(store): pass state to getters as first argument

BREAKING CHANGE: getters now receive the state as their first argument and it's properly typed so you can write getters with arrow functions:

```js
defineStore({
  state: () => ({ n: 0 }),
  getters: {
    double: state => state.n * 2
  }
})
```

To access other getters, you must still use the syntax that uses `this` **but it is now necessary to explicitely type the getter return type**. The same limitation exists in Vue for computed properties and it's a known limitation in TypeScript:

```ts
defineStore({
  state: () => ({ n: 0 }),
  getters: {
    double: state => state.n * 2,
    // the `: number` is necessary when accessing `this` inside of
    // a getter
    doublePlusOne(state): number {
      return this.double + 1
    },
  }
})
```

For more information, refer to [the updated documentation for getters](https://pinia.esm.dev/core-concepts/getters.html).