collations

Analysis:
When we have negative index, the value in array_counter[] array is going to
be -1 at some point ( because in case of negative index in json path, the
initial value for a path with negative index is -<size_of_array>, and as we
move forward in array while parsing it and finding path, this value
increments). Since SKIPPED_STEP_MARK, is maximum uint value, it gets
compared to some int value in the array and eventually equates to -1
and messes with path.
Fix:
Make SKIPPED_STEP_MARK maximum of INT32.

btr_cur_need_opposite_intention(): Check also page_zip_available()
so that we will escalate to exclusive index latch when a non-leaf
page may have to be split further due to ROW_FORMAT=COMPRESSED page
overflow.

Tested by: Matthias Leich

Derived table creation code would call Field::make_new_field() which would
memcpy the Field object from the source table, including Field::read_stats.

But the temp. table as a whole had table->stats_is_read=false. Which was
correct but not consistent with Field::read_stats and caused an assertion.

Fixed by making sure that Field::read_stats=NULL for fields in the new
temporary (i.e. work) tables.