PostgreSqlType - Change "PGInterval" to "String

[griffio]

PostgreSqlType INTERVAL was initially mapped as PgInterval

https://github.com/cashapp/sqldelight/blob/431caee2a99885719b1a43db2e08ef16a3b64af8/dialects/postgresql/src/main/kotlin/app/cash/sqldelight/dialects/postgresql/PostgreSqlType.kt#L21

This 🥨 changes the mapping to String as org.postgresql.util.PgInterval is a JDBC type and would be consistent with JSON, TSVECTOR, XML type mapping. The client can use a type adapter for the string value to a desired platform type - Duration, Period ... etc. Docs page updated with type mapping

Requirement -
Write to an Interval column using setObject Other, as this is required for it to interpret as an interval type
Read from an Interval column usinggetString, this is formatted using the intervalstyle* PG client option

• For example, "-c intervalstyle=iso_8601" can be set on the client connection options and used with a custom kotlin.time.Duration column adapter as intended by SqlDelight to encode/decode iso interval values

Note:
Future Developments

• PostgreSqlType dialect type should not reference JDBC (java.sql) types as not all drivers are JDBC
• There should be specific driver dialect subclasses (PostgreSql JDBC, PostgreSql R2DBC) without the need to create a new dialect
  • e.g PostgreSql JDBC has PGobject types for JSON, Interval that setObject can use
  • e.g PostgreSql R2DBC needs a specific codec class for JSON type that currently cannot be used in statements