Added checks of ArrowExpressionClausSyntax to ensure correct spacing

[bexxx]

Added checks of ArrowExpressionClausSyntax to ensure correct spacing + unit test.
Fixes already worked with the new diagnostic locations (yeah!).

This fixes issue #1764.

[codecov-io]

Current coverage is 79.43%

Merging #1783 into master will decrease coverage by -0.02% as of 038d6d3

@@            master   #1783   diff @@
======================================
  Files          548     548       
  Stmts        32875   32918    +43
  Branches      9111    9116     +5
  Methods                          
======================================
+ Hit          26120   26147    +27
  Partial       5300    5300       
- Missed        1455    1471    +16

Review entire Coverage Diff as of 038d6d3

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[vweijsters]

👍 Looks good to me