This WL defines INFORMATION_SCHEMA (I_S) system view over DD tables,
representing a I_S table. This will eliminate the need of preparing a
temporary table for each I_S table during execution and enable faster
execution of I_S queries.

A. Functional changes introduced:
---------------------------------
A.1) Implements following I_S tables as a system view.

  CHARACTER_SETS
  COLLATIONS
  COLLATION_CHARACTER_SET_APPLICABILITY
  SCHEMATA
  TABLE_NAMES
  TABLES
  VIEWS
  COLUMNS
  STATISTICS
  KEY_COLUMN_USAGE
  TABLE_CONSTRAINTS

A.2) Implements following SHOW commands to use A.1).

  SHOW CHARSET
  SHOW COLLATION
  SHOW DATABASES
  SHOW TABLES
  SHOW TABLE STATUS
  SHOW COLUMNS
  SHOW KEYS/INDEXES
  SHOW STATISTICS
  DESCRIBE

A.3)
  Introduces a session variable 'information_schema_stats' that
  enables use to decide how to get the table/index dynamic
  statistics. Setting it to 'latest' would get latest statistics
  from storage engine. And setting it to 'cached' would get
  statistics stored in mysql.table_stats/index_stats. These are two
  new DD tables introduced by this WL. These tables are updated
  when user runs ANALYZE TABLE on a table. For more details see HLS
  2.1.4) and 2.1.12).

A.4) Introduced following new DD columns, see HLS 2.1.8) for more
     details.

  COLUMNS.COLUMN_KEY
  COLUMNS.COLUMN_TYPE
  COLUMNS.DEFAULT_VALUE_UTF8
  TABLES.ROW_FORMAT

A.5)
  Implements special handling for SHOW COLUMNS/KEYS for temporary
  tables as the meta data of temporary tables are not stored in DD.

A.6)
  I_S tables are temporary tables on 5.7. This make them
  possible to access under LOCK TABLE mode with explicitly
  locking I_S tables. Now with this WL, the query execution
  procedure fails to process I_S system view as the under laying DD
  table are not locked.

  So, this WL makes the SQL server to open the DD tables used by
  a I_S system view without requiring them to be locked explicitly.

B. Performance improvements:
----------------------------

See mysql wiki page WL6599_I_S_performance_with_data_dictionary
for more details. (HLS section 5)

C. Compatibility issues:
------------------------
There are few differences in the way mysql server would behave
after this WL. The detailed list of these change in behavior is
listed under HLS section 6).

D. Source files:
----------------
Most of code changes are placed in sql/dd/info_schema folder.

* Refer code in sql/dd/info_schema/show.* to know how SHOW
  commands are implemented.

* Refer code in sql/dd/info_schema/stats.* to know how the
  retrieval of dynamic statistics are implemented.

E. Related WL's and Bugs:
-------------------------

* WL#7167 Change DDL to update rows for view columns in
  DD.COLUMNS and other dependent values.

  I_S.COLUMNS will get column meta data for views from
  mysql.columns. The view's column meta data are stored in
  mysql.columns by this WL. The WL takes care of enabling several
  test cases that is disabled by this WL#6599. So WL#6599 and
  WL#7167 would be pushed together. They are QA'ed together.

* WL#7464 - InnoDB: provide a way to do non-locking reads.
  This WL enables execution of I_S queries do to non-locking reads.

* WL#8232 - New data-dictionary: change approach to table
            row_format and index algorithm validation/handling

Upcoming WL:
* WL#9494   Implement INFORMATION_SCHEMA system views for
            SP/TRIGGERS/EVENTS/REFERENTIAL_CONSTRAINTS

* WL#9495   Update schema tables of dynamic plugins into data
            dictionary.

The following bugs would be fixed by this WL:
  Bug#11748044
  Bug#13878164

F. Disabled tests:
------------------

thread_pool.thread_pool_i_s : Would be fixed by WL#9495.
i_innodb.innodb_bug14150372 : WL6599_INNODB_SPORADIC