Add "handle-as" hint provider

Replace the enum provider by a more general purpose provider that can
substitute the type of the property for the purpose of auto-completing
the values.

"handle-as" can be used for enums but for any type that the IDE
understands such as locale, charset, mime-type and Spring's resource
abstraction.

Closes gh-3457

spring-boot-autoconfigure/src/main/resources/META-INF/additional-spring-configuration-metadata.json

@@ -229,7 +229,7 @@
     "name": "spring.jooq.sql-dialect",
     "providers": [
       {
-        "name": "enum",
+        "name": "handle-as",
         "parameters": {
           "target": "org.jooq.SQLDialect"
         }