Shorten some VARCHAR attributes to a more reasonable length.

INNODB_METRICS: Rename the column STATUS to ENABLED, and make it Boolean.

Replace with INT(1) many Boolean attributes that were declared as VARCHAR
containing 'NO','YES','disabled','enabled','Uninitialized','Initialized'.

Replace some VARCHAR attributes with ENUM.

Replace some BIGINT with INT when 32 bits are sufficient.

Remove INNODB_SYS_TABLESPACES.SPACE_TYPE. The type of a tablespace
can be derived from the tablespace ID. A fixed number is used for
the system tablespace and the temporary tablespace. All other tablespaces
are single-table or single-partition tablespaces.

i_s_locks_row_t::lock_type, lock_get_type_str(): Remove.
This is a redundant field. Table and record locks can be
distinguished by whether i_s_locks_row_t::lock_index is NULL.

fill_trx_row(): Do not unnecessarily copy the constant strings that
trx->op_info is pointing to.

i_s_locks_row_t::lock_mode: Replace string with integer.

lock_get_mode_str(), lock_get_trx_id(), lock_get_trx(): Remove.

field_store_ulint(): Remove.