Fix issue 866: LexicalPreservingPrinter: Unsupported operation - remove

[ftomassetti]

This fix #866.
The PR is built on top of #929 and #930

We introduce a new CsmElement named CsmMix to represent elements that can have any order. They require a specific handling in Difference.apply. We basically considere the CsmMix before the change, after the change and the order of elements in the text trying to figure out the most natural way to change the text.

Additionally we need also to adapt space around in certain cases.

These three PRs combines should fix a few things in the lexical preservation. It is probably not 100% perfect but the number of tests is growing (203) and it should eventually stabilize. There are hard things related to indentation and space reconciliation.

In the long term I hope we root out all bugs, we grow our test base and then in 4.0 we can improve the whole design.

[coveralls]

Coverage increased (+0.3%) to 66.974% when pulling 6125d1a on ftomassetti:issue866 into 0e768bf on javaparser:master.

[matozoid]

Mergey merge merge?

[coveralls]

Coverage increased (+0.3%) to 66.924% when pulling 4543ed1 on ftomassetti:issue866 into e999169 on javaparser:master.

[ftomassetti]

Rebased after merging #933

[coveralls]

Coverage increased (+0.3%) to 66.936% when pulling a335935 on ftomassetti:issue866 into 5523c58 on javaparser:master.

[coveralls]

Coverage increased (+0.3%) to 66.94% when pulling 7d55cf4 on ftomassetti:issue866 into 5523c58 on javaparser:master.