Support PostgreSQL

Problem/Motivation

The module currently has a compatibility issue when used with PostgreSQL.
I get this error if both "Case sensitive" and "Match whole word" are both selected when using postgresql version 16.14 (tested) or higher (also tested)

SQLSTATE[2201B]: Invalid regular expression: 7 ERROR: 
invalid regular expression: quantifier operand invalid: 
SELECT "base_table"."vid" AS "vid", "base_table"."nid" AS "nid"
FROM "c1pgags12dev"."node" "base_table"
INNER JOIN "c1pgags12dev"."node_field_data" "node_field_data"
  ON "node_field_data"."nid" = "base_table"."nid"
INNER JOIN "c1pgags12dev"."node__body" "node__body"
  ON "node__body"."entity_id" = "base_table"."nid"
 AND "node__body"."langcode" = :langcode0 WHERE ("node_field_data"."type" = :db_condition_placeholder_1) 
 AND ("node_field_data"."langcode" = :db_condition_placeholder_2) 
 AND ("node__body"."body_value"::text ~* :db_condition_placeholder_3); 
Array ( [:db_condition_placeholder_1] => empl [:db_condition_placeholder_2] => en [:db_condition_placeholder_3] => (?-i)[[:<:]]tfoot[[:>:]] [:langcode0] => en ) in Drupal\Core\Entity\Query\Sql\Query->result() (line 288 of core/lib/Drupal/Core/Entity/Query/Sql/Query.php).

Proposed resolution

See merge request and/or patch
Support Postgres.

Remaining tasks

Review and test patch.

User interface changes

Allows selecting "Case insensitive" option WITH "Match word" without crashing WSOD.

API changes

None.

Data model changes

None.