Improved indentation handling of IndentationHelper.GetIndentationSteps

[vweijsters]

Fixes #1036
Fixes #1037

For #1037 I've implemented a fourth option: rounding. For indentation size 4 this means: 0-1 no indent, 2-3 single indent. This is my personal preference, as it is forgiving when there is one space to many / little. I'll be happy to adapt it if wanted.

[codecov-io]

Current coverage is 79.44%

Merging #1751 into master will not affect coverage as of e3ab60a

@@            master   #1751   diff @@
======================================
  Files          546     548     +2
  Stmts        32764   32797    +33
  Branches      9078    9083     +5
  Methods                          
======================================
+ Hit          26029   26055    +26
- Partial       5273    5278     +5
- Missed        1462    1464     +2

Review entire Coverage Diff as of e3ab60a

Powered by Codecov. Updated on successful CI builds.

[sharwell]

This seems fine.

I do wonder if we should instead simply use the previous indentation string unaltered, rather than trying to rewrite it using the currently configured indentation characters. But that is a separate issue.