[PropertyAccess] Refactored PropertyAccessorTest
[PropertyAccess] Refactored PropertyAccessorCollectionTest
[PropertyAccess] Added isReadable() and isWritable()
[PropertyAccess] Fixed CS and added missing documentation
[PropertyAccess] Removed the argument $value from isWritable()

To keep isWritable() and setValue() consistent, the exception thrown when only
an adder was present, but no remover (or vice versa), was removed.
[PropertyAccess] Added missing exceptions to phpdoc
feature #10570 [PropertyAccess] Added isReadable() and isWritable() (webmozart)

This PR was merged into the 2.5-dev branch.

Discussion
----------

[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.

Commits
-------

f7fb855 [PropertyAccess] Added missing exceptions to phpdoc
9aee2ad [PropertyAccess] Removed the argument $value from isWritable()
4262707 [PropertyAccess] Fixed CS and added missing documentation
6d2af21 [PropertyAccess] Added isReadable() and isWritable()
20e6bf8 [PropertyAccess] Refactored PropertyAccessorCollectionTest
0488389 [PropertyAccess] Refactored PropertyAccessorTest