2.0.6 - CAST function improvements

Restricts the target type of the CAST DQL function to the supported type names and to a numeric
length or precision, so a query expression can no longer place arbitrary text into the type position
of the generated SQL.

What is changed

• A CAST expression is accepted only when its target type is one of the documented type names. A name that merely begins with a supported one, such as timestamp or int8, is now rejected as unsupported.
• A parenthesised length or precision is accepted only as non-negative integers, so CAST(expr as char(5)) and CAST(expr as decimal(10, 2)) keep working and any other content is reported as a syntax error.
• jsonb is a supported type name in its own right, so a cast to it is accepted and renders as it did before.
• A type that carries a length or a precision is mapped to the platform's own type name, so CAST(expr as string(12)) produces varchar(12) on PostgreSQL and char(12) on MySQL instead of being passed through unchanged.
• Every supported type given without a length or a precision produces the same SQL as before on both platforms.

Impact

• Applications that rely on a platform-specific type spelling accepted only because it shares a prefix with a supported name (timestamp, timestamptz, int8) now get a syntax error and have to use one of the supported type names.
• Queries that use the documented types, with or without a length or a precision, are unaffected, and the SQL generated for them is unchanged.
• The dependency requirements are untouched, so a release from this branch installs alongside doctrine/orm 2.8 with doctrine/lexer 1 and doctrine/dbal 2.12, which is the combination OroPlatform 4.2 is fixed to.
• No configuration changes or upgrade steps are required.