Deprecate wpdb::escape()

[nacin]

wpdb::escape() has been used by core and plugins as a generic addslashes() alias. That isn't ideal. In #21767 we've removed all improper usage of wpdb::escape(), at which point everything now uses either wpdb::prepare() or esc_sql() (for database escaping) or wp_slash() (for the unfortunate need to generically slash).

We should deprecate wpdb::escape(). In the process, esc_sql() should become a wrapper for real escape, because it would be crazy and wrong to be using esc_sql() in a non-SQL context.

This came out of work by the WP security team.

[nacin]

In 24718:

Deprecate wpdb::escape() in favor of wpdb::prepare() and esc_sql(). fixes #24774.

[nacin]

In 24724:

Ensure _deprecated_function() exists before calling it. wpdb currently does not have a full functions.php dependency, and this can break external inclusions. see #24774.

[bcworkz]

ChrisWiegman and jdgrimes fixed the primary Codex entries last August. I found a few more stray entries in Function Reference. Any remaining mentions are about it being deprecated.