Improve makeAdl/Db scripts

[xiaoqiangwang]

• Check recursively AccessMode for nodes with pValue defined. e.g. FirmwareVerMinor refers RegFirmwareVerMinor, which has the AccessMode defined. https://github.com/areaDetector/ADGenICam/blob/da91e915f6373f74bbc04e1c0c188d0ff3aa3870/xml/AVT_Mako_G507B.xml#L383-L388 https://github.com/areaDetector/ADGenICam/blob/da91e915f6373f74bbc04e1c0c188d0ff3aa3870/xml/AVT_Mako_G507B.xml#L3412-L3419
• Add String nodes support. According to GenICam Standard section 2.8.12, String is of variable length compared to StringReg. Both are possibly writable, e.g. DeviceUserID https://github.com/areaDetector/ADGenICam/blob/da91e915f6373f74bbc04e1c0c188d0ff3aa3870/xml/AVT_Mako_G507B.xml#L3495-L3502
• Add IntReg nodes support. It is often used for internal features. But in a Basler acA1300-200uc camera, it is used for EventExposureEnd feature.

  <IntReg Name="EventExposureEnd" NameSpace="Standard">
  <ToolTip>Unique identifier of the Exposure End event.</ToolTip>
  <Description>Unique identifier of the Exposure End event. Use this parameter to get notified when the event occurs.</Description>
  <DisplayName>Event Exposure End</DisplayName>
  <Visibility>Expert</Visibility>
  <Address>0x2</Address>
  <Length>2</Length>
  <AccessMode>RO</AccessMode>
  <pPort>EventExposureEndEventPort</pPort>
  <Sign>Unsigned</Sign>
  <Endianess>LittleEndian</Endianess>
  </IntReg>