[PropertyAccess] Added isReadable() and isWritable()

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | yes
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #8659
| License       | MIT
| Doc PR        | symfony/symfony-docs#3729

This PR introduces BC breaks that are described in detail in the UPGRADE file. The BC breaks conform to our policy. They shouldn't affect many people, so I think we can safely do them.