Prior versions of `CommonPrintUtils.balanceParens` treated parens in string
constants just like parens in regular Scala code which resulted in bugs like
ticket #1002088. This commit improves the aforementioned function, that also
played a prominent role in ticket #1002166, by delegating counting parens
to a helper function, that handles comments and string constants properly.

Fixes #1002088

The term "brackets" is used for "<>", "()", "{}" and "[]", while parens usually
refers to "()" and "{}" only. As the function in question accepts the brackets
as parameters, "brackets" is more appropriate than "parens".

`CommonPrintUtils.balanceBrackets` used to contain some code that was meant to
add missing closing brackets directly after the last closing bracket, instead of
just appending them to the layout. Given the fact that the code was broken anyway,
(it didn't consider comments, string constants, etc.), all tests pass without it,
and the original author thinks that it's not needed, it seems safe to remove it.