Remove fixUpStack to fix blank paragraph insertion bug

The fixUpStack is actually redundant code and closingStack
and openingStack handle all our cases. It was causing the
insertion to try to correct balance itself in the middle
of inserting two paragraphs, causing the creation on an
empty paragraph between them.

Added a test case for the fix and other cases to make
sure removing fixUpStack hasn't caused problems.

Bug: 46800

Change-Id: I35e54165709ac56e8116359a7c3b487eecf08ff7
Merge "Remove fixUpStack to fix blank paragraph insertion bug"