This patch implements I_S.FILES as a system view over data
dictionary tables, and remove 5.7 code that uses a temporary
table to represent I_S view.

Following changes are made in the patch:

* Define a system view over data dictionary tables representing
  I_S.FILES.

* Remove 5.7 code from sql_show.cc for I_S.PARTITIONS.

* Add new handler API handlerton::get_tablespace_statistics_t with
  following signature.

  typedef bool handlerton::(*get_tablespace_statistics_t)(
                  const char *tablespace_name,
                  const dd::Properties &ts_se_private_data,
                  ha_tablespace_statistics *stats);

  This handler provides following data to I_S.FILES,
    ID,
    TYPE,
    LOGFILE_GROUP_NAME,    // To be used by NDB
    LOGFILE_GROUP_NUMBER,  // To be used by NDB
    FREE_EXTENTS,
    TOTAL_EXTENTS,
    EXTENT_SIZE,
    INITIAL_SIZE,
    MAXIMUM_SIZE,
    AUTOEXTEND_SIZE,
    VERSION,     // To be used by NDB
    ROW_FORMAT,  // To be used by NDB
    DATA_FREE,
    STATUS

* Add new internal native functions to fetch above statistics for
  I_S.FILES.
    INTERNAL_TABLESPACE_ID()
    INTERNAL_TABLESPACE_TYPE()
    INTERNAL_TABLESPACE_FREE_EXTENTS()
    INTERNAL_TABLESPACE_TOTAL_EXTENTS()
    INTERNAL_TABLESPACE_EXTENT_SIZE()
    INTERNAL_TABLESPACE_INITIAL_SIZE()
    INTERNAL_TABLESPACE_MAXIMUM_SIZE()
    INTERNAL_TABLESPACE_AUTOEXTEND_SIZE()
    INTERNAL_TABLESPACE_DATA_FREE()
    INTERNAL_TABLESPACE_STATUS()

* Added new per statistics cache class dd::info_schema::Tablespace_statistics
  to store statistics retrived by SE to be used when processing
  single row of a I_S query. This avoids internal native functions to
  invoke SE API only once per row.

* Renamed dd::info_schema::Statistics_cache to
  dd::info_schema::Table_statistics because we now have not only table
  statistics by tablespace statistics to be cached.

* Added ORDER BY clauses in some of I_S query to force order of
  tuple returned. Because, now the optimizer returns the rows and
  not read from temporary table as in 5.7 I_S design.

* Add new error message that can be reported when by I_S.FILES when
  tablespace is missing when fetching tablespaces statistics.

* Remove part of test case in main.information_schema. Because,

  - The problem reported back then is only applicable for 5.7
    code.

  - The output of EXPLAIN ... <select on I_S system view> goes
    through optimizer and then plan return might vary.

* Suppress additional warnings generated which report missing tablespaces.
  This happens now, because of one of following,

  case1) If .ibd is copy by user manually on file-system, then DD is not
         updated and hence I_S do not see it. The 5.7 behavior is that it looks
         at .ibd file in file-system and not in DD.

  case2) Once I_S query execution starts we see the content of DD as of the
         time I_S query started. If there is a new tablespace added or removed,
         then I_S would not see it.

* MySQL 5.7 does prefix './' with all .ibd files which are to be stored in
  data directory. MySQL 8.0 had skipped it. I_S.FILES system view prefixes
  './' if filename does not have explicit patch already specified by user.

  Perhaps this should need a fix in server or innodb. Probably the concern
  raised in Bug#26518545 is the same. We might need to change
  I_S.FILES.FILE_NAME definition after the bug fix.

* Test case for Bug#23477214 is removed now. Because the race condition
  does not apply now after I_S.FILES becomes a system view.

* Record result files with capital I_S column names, this is expected. See
  WL6599 for more info.

* We now show 1024 character of partition comment string, unlike just 80
  characters shown in 5.7 by I_S.