プロパティーのタイプ (読み取り専用)
Property type determines which of the "value" variable accessors are valid.
For example, only boolValue is valid for SerializedPropertyType.Boolean
For numeric types SerializedPropertyType.Float and SerializedPropertyType.Integer, the best accessor can be determined with numericType,
for example floatValue should be used for SerializedPropertyNumericType.Float and doubleValue should be used for SerializedPropertyNumericType.Double.
Additional resources: SerializedPropertyType, numericType.