migrate some junit 4 suites to junit 5

[carstenartur]

What it does

As suggested in #1631 (comment) here we have a first try to update the suites from junit 4 to junit 5 so that step by step upgrade of tests to junit 5 or even a mix of junit 4 and junit 5 based tests is possible.

Unfortunately there are two issues currently:

1. baseline and build for org/eclipse/jdt/internal/ui/text/correction/QuickAssistProcessorUtil.class have different contents
2. baseline and build for org/eclipse/jdt/internal/corext/fix/StringConcatToTextBlockFixCore$StringBufferFinder.class have different contents

How to test

Author checklist

• I have thoroughly tested my changes
• The change is following the coding conventions
• I have signed the Eclipse Contributor Agreement (ECA)

[carstenartur]

@akurtakov can you have a look if this is what you suggested?

[akurtakov]

I haven't done detailed review but this is aligning with the overall idea - make suites JUnit5 ones so individual tests can be added/migrated to JUnit 5 later.

[akurtakov]

Same number of tests, tests succeed, only a small portion of new code which looks wrong to me.
@jjohnstn would you please double check this PR?

[jjohnstn]

Hi @akurtakov I did look at it and was waiting for your comments as @carstenartur was asking if it met your expectations. I too noticed that same number of tests ran and succeeded. Does this patch make it possible to have the explicit encoding tests added instead of forcing manual execution?