Add `equals`/`hashCode` support for `Unpaged`

[bigluds]

It seems that my JUnit tests using Mockito fails because the Unpaged does not fully support equals/hashcode sementic when Sort is specified.

In the tests below, the tests PageableTests#testEqualsOnUnpagedUnsortedCase1 and PageableTests#testEqualsOnUnpagedUnsortedCase2 are success (because there is it the same instance) while the last one PageableTests#testEqualsOnUnpagedSorted fails due to a leak on equals/hashcode sementic (because equals/hashcode sementic is not implemented).

So using Mockito on a repository with Pageable fails when I use a Pageable.unpaged(Sort). Could you, please review the code to correct this issue.

package com.myapp;

import org.assertj.core.api.Assertions;
import org.junit.jupiter.api.Test;
import org.springframework.data.domain.Pageable;
import org.springframework.data.domain.Sort;

public class PageableTests {

    @Test
    void testEqualsOnUnpagedUnsortedCase1() {
        Assertions.assertThat(Pageable.unpaged()).isEqualTo(Pageable.unpaged());
    }

    @Test
    void testEqualsOnUnpagedUnsortedCase2() {
        Assertions.assertThat(Pageable.unpaged(Sort.unsorted())).isEqualTo(Pageable.unpaged(Sort.unsorted()));
    }

    @Test
    void testEqualsOnUnpagedSorted() {
        Assertions.assertThat(Pageable.unpaged(Sort.by("code"))).isEqualTo(Pageable.unpaged(Sort.by("code")));
    }

}```

[bigluds]

Below the JUnit tests results:

[mp911de]

Thank you for the enhancement proposal. It makes sense to implement both methods for equality checks.