Rework Mylyn Doc tests that requires package-local access

[ruspl-afed]

After switching from bundle to eclipse-plugin + eclipse-test-plugin we have a number of troubles with accessing package-local members during tests. Although we can use fragments to solve this, it may be better to improve implementation and tests instead.
It is good to have package local members, and strictly speaking the amount of public members for a package should be minimal
However, tests should be focused rather on testing type's contract than on accessing its internals.

The list of tests to be revived:

• DefaultSplittingStrategyTest
• HtmlEntitiesTest
• HtmlParserTest
• ServiceLocatorTest
• WikiToDocTaskTest