fix: EXPOSED-116 UUID conversion error with upsert in H2

[bog-walk]

Using a UUID column as a key id constraint in H2's MERGE INTO .. USING statement fails with:

org.h2.jdbc.JdbcSQLDataException:
Data conversion error converting "U&'\\fffdK\\fffdS\\001bJr\\fffdG%\\fffdE\\00100\\fffd' (TESTER: ""ID"" UUID NOT NULL)";

This error occurs because the statement uses a derived column list to merge ON (T.ID=S.ID), so the UUID as a ByteArray stored in T.ID needs to be converted internally to compare with the String in S.ID (from generated SQL). This error goes away if a regular integer id column is used or if the key constraint is swapped with another non-UUID type.

The error also goes away if an identical MERGE statement is placed in exec() directly, indicating that the issue lies with how Exposed sends UUID values to the H2 database.

Switching the sent value from a ByteArray to a String allows comparison without conversion. A String is still one of 3 acceptable ways to store a UUID in H2 and sending a String still results in a UUID being retrieved back from the database (via valueFromDB() and readObject()).

Additional:

• Because H2_Oracle is delegating to Oracle, it uses Oracle's RAW(16) type instead of H2's UUID type and leads to a second error:

org.h2.jdbc.JdbcSQLSyntaxErrorException:
Values of types "BINARY VARYING(16)" and "CHARACTER VARYING" are not comparable;

To resolve this, H2_Oracle could also be made to use the Oracle-specific UPSERT statement, but this syntax fails when sent to H2. Instead, the compatibility mode now uses the H2DatatypeProvider overrides.