Add Q_PROPERTY to all QtSql (kernel) classes

Clean up the documentation of all sql classes by using Q_PROPERTY instead documenting the getter and setter separately.

• QSqlDatabase
  • QSql::NumericalPrecisionPolicy numericalPrecisionPolicy
• QSqlDriver
  • QSql::NumericalPrecisionPolicy numericalPrecisionPolicy
• QSqlError - no setter so no changes needed
• QSqlField - no QObject, added Q_GADGET
  • QVariant value
  • QVariant defaultValue
  • QString name
  • QString tableName
  • QMetaType metaType
  • RequiredStatus requiredStatus
  • bool readOnly
  • bool generated
  • bool autoValue
  • int length
  • int precision
• QSqlIndex
  • cursorName
  • name
• QSqlQuery
  • bool forwardOnly
  • bool positionalBindingEnabled
  • QSql::NumericalPrecisionPolicy numericalPrecisionPolicy
• QSqlRecord - no properties, access only through indexed setter/getter
• QSqlResult
  • bool forwardOnly --> internal, no property
  • bool positionalBindingEnabled --> internal, no property
  • QSql::NumericalPrecisionPolicy numericalPrecisionPolicy --> internal, no property