- The logic to take the enclosing element of the completion context, and
arrive at a "better" node, should always consider nodes that have the
same start position as the best node encountered so far. Such nodes are
likely to be smaller (since they're discovered later in the AST
traversal), and less likely to overlap with the invocation offset
- In JavaPostfixContext#findBestASTNodeSelection(ASTNode), take into
account where the completion tokens (if any) were entered to avoid
including nodes that overlap with the invocation offset
- Add testcase

Change-Id: I2fdc94c9e76556ad7f6011a575cc53657c4b3cdb