cleanup: freshen up CREATE SERVER code

* pass LEX_STRING's from the parser, don't ignore the length only to strlen later
* init LEX::server_options only for SERVER commands, not for every statement
* don't put temporary values into a global persistent memroot

but really it's just scratching a surface
MDEV-6311 Add errors on CREATE SERVER

fail CREATE SERVER foreign data wrapper is "mysql"
and neither HOST nor SOCKET are specified.

Also default PORT to 3306 (again, only for foreign
data wrapper "mysql")
cleanup: ptr_cmp

1. don't cast size_t* to int*
2. remove long obsolete register specifier
cleanup: reuse MY_CHECK_AND_SET_COMPILER_FLAG in sphinx/CMakeLists.txt
cleanup: s/const CHARSET_INFO/CHARSET_INFO/

as CHARSET_INFO is already const, using const on it
is redundant and results in compiler warnings (on Windows)
oqgraph cleanup: remove casts
MDEV-5871 support assisted discovery in oqgraph v3
MDEV-6894 Enable SEQUENCE engine by default
MDEV-6980 OUT parameters in PREPARE

revert the patch for "out parameters in prepare"
MDEV-6895 switch to dynamic libjemalloc.so
MDEV-6979 simplify trigger rules for RBR triggers

Rows_log_event::write_row - don't optimize DELETE+INSERT
into UPDATE if RBR triggers are used
MDEV-6999 Remove or deprecate unused variables
a case of uninitialized variable
fix a comment
update 32-bit rdiff's
cleanup: sql_plugin.cc

* test for opt->name being non-NULL *before* dereferencing it
* remove unused argument in cleanup_variables()
* simplify
don't load plugin of unsupported types
remove unsupported service file
cleanup: bool_variable= -1; -> bool_variable= true;
cleanup: normalize LEX_USER to get rid of different representation of the same thing

  username IDENTIFIED BY PASSWORD xxx
  username IDENTIFIED VIA mysql_native_password USING xxx
  etc

also check for valid strlen(xxx)