Merge branch 'hotfix/#6877-zend-session-event-manager-dependency'

Close #6877
Close #6818
Merge branch 'hotfix/#6871-memcache-return-false-on-failure-perf-improvement'

Close #6871
Merge branch 'hotfix/#6778-zendxml-suggestion-in-zend-json'

Close #6778
Return the text value in _ array key

If element has attributes & string value until now the string value was ignored & lost, I added the _ index so that it also returns the string value along with the attribute names
Fix CS + reduce branch depth
Reproducing test case for #6279
Add abstract Ddl Column classes to handle variable length data types
Change floating point Ddl columns to inherhit from
AbstractPrecisionColumn
Change character Ddl column classes to inherhit AbstractLengthColumn
Removed unused $length property from Integer Ddl column class
Reduce code duplication in temporal ddl column classes

Fixes missing DEFAULT value in expression data
Fix BLOB Ddl column erroniously allows length, adds Binary with length
Reduce code duplication in Booloan Ddl column class

Purposely ignore $isNullable from parent by resetting it in
getExpressionData()
Reduce code duplication in the Text Ddl Column class
Add Ddl column classes to support DATETIME, TIMESTAMP, and VARBINARY
Adjust Dbl Column class test expectations

* NOT NULL should be in the spec like DEFAULT
* Type is never in the spec (always second param)
* Float column should have FLOAT type
Move NOT NULL into the spec for Ddl Columns
Allow length based column types to be constructed without length
Move the Integer column construction signature to the parent Column
Use the parent Column constructor for the length/precision abstracts