Simplify several methods in PyCharm utility classes

* Use Collections.addAll(xs, arr) instead of xs.addAll(Arrays.asList(arr))
* QualifiedName#toString is the same as StringUtil.join(qn.getComponents(), ".")
* PyUtil.as is the same as ObjectUtils.tryCast
* Several methods in PyUtil contain redundant trailing conditions
Remove "unittest" package from mock SDK, include it in test data instead
IDEA-COMMUNITY-CR-1085 Handle badly formatted imports with whitespaces before/after dots
Remove PyUtil.turnDirIntoPackageElement in favor of PyUtil.getPackageElement
CodeInsightTestFixture.testHighlighting(java.lang.String...): fix javadoc
NPE in SMTestProxy
extract method: allow to extract from fragment with different exit points which all are @NotNull
include test for acceptable return types in 'extract' suite
extract method: do not suggest object when multiple returns are used without output variable
extract method: do not suggest primitive type when 'return null;' should be inserted
don't report negated compile-time constants as always true/false (IDEA-118388)
don't return inferred annotations that will be neglected anyway (e.g. on overrideable methods)
contract/nullity light inference from source: handle autoboxing in return values
nullity inference from source dfa: handle autoboxing in return values