…ervice for string does not allow setting charset

(commit 21056bf) from Oracle MySQL 9.0 tree.

Bug#36430572 Bug#36491859: mysql_stored_program service for string does not allow setting charset

- Add services for setting string for argument and return value which supports setting charset. However, for existing string types, the charset which is set at creation is used instead of the one set in these services.
- Set Item name to be empty string for Item_string.

Change-Id: I595a3d6e352af9632bb5473866e1c775f80e15f4

…n't work for non-string types

(commit aabae02) from Oracle MySQL 9.0 tree.

Bug#35517611 HCS-8941 SP string argument get doesn't work for non-string types

- Allocate a buffer from current_thd memroot and copy the string to this buffer. The return value is this buffer.

Change-Id: I831185379fed78698daf95cdf4d60b365d458cb4

…work for non-string types

(commit 632a740) from Oracle MySQL 9.0 tree:

Postfix Bug#35517611: SP string argument get doesn't work for non-string types

Change-Id: Ica4b6d1fb174cb572e79f6b30e5e0b7ce32889fc

https://perconadev.atlassian.net/browse/PS-9190

Implement component that adds to Percona Server for MySQL support
of Stored Functions and Procedures written in JS language or,
more formally, ECMAScript by employing Google's V8 engine.

This is the first commit in a series which implements basic
functionality such as:

- Creation/dropping of JS stored functions and procedures.
- Execution of stored functions/procedures.
- Support for return values for stored functions, IN and OUT parameters for procedures,
  including charset and type mapping/conversions.
- New global dynamic privilege for JS routine creation and its checking.
- Correct isolation of between different security contexts.

First pack of post-review fixes.

Second pack of post-review fixes.

Third pack of post-review fixes.

Fourth pack of post-review fixes.