RFR: Extend API to support JOL IntelliJ Idea plugin

[Sergey Ponomarev]

[JOL Intellij Idea Plugin](https://github.com/stokito/IdeaJol)  internally uses JOL.
Internally in the
[PsiClassAdapter](https://github.com/stokito/IdeaJol/blob/master/src/main/java/com/github/stokito/IdeaJol/PsiClassAdapter.java)
it makes exactly the same as `org.openjdk.jol.info.ClassData#parse` but it creates the ClassData from Idea's AST/Psi
tree instead of raw `Class`. Unfortunately to be able to do this we need to extend API a little bit.

Here is a short list of changes that I did:
1. Added an overloaded method ClassData.addSuperClassData(ClassData) so I can create an instance of `ClassData`
2. Added `lossesInternal`, `lossesExternal` and `lossesTotal` fields to `ClassLayout` so they calculated only once on
instance creation and then can be accessed multiple times via geters by JTable  3. `FieldData.create()` internally
evaluate if the field is contended but we do this based on Psi tree. So we need to open and make public the `FieldData`
constructor.

-------------

Commit messages:
 - ClassLayout: rename createClassLayout() to create()
 - ClassLayout: add javadocs
 - FieldData: expose full FieldData.create() constructor
 - ClassLayout: rename loses variables for clearness
 - ClassDataTest: add newline
 - ClassLayout: calculate loosed bytes inside of createClassLayout()
 - ClassLayout: call checkInvariants() from createClassLayout() instead of constructor
 - Replace ClassLayout constructor with factory method
 - ClassData: Return List instead of Collection
 - ClassData: introduce addSuperClassData(ClassData)

Changes: https://git.openjdk.java.net/jol/pull/4/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jol&pr=4&range=00
  Stats: 196 lines in 7 files changed: 169 ins; 10 del; 17 mod
  Patch: https://git.openjdk.java.net/jol/pull/4.diff
  Fetch: git fetch https://git.openjdk.java.net/jol pull/4/head:pull/4

PR: https://git.openjdk.java.net/jol/pull/4