[docs] Build with JavaDoc 17 and add missing docs (#6220)

Co-authored-by: Sam Carlberg <sam.carlberg@gmail.com>

ntcore/src/main/native/include/networktables/NTSendableBuilder.h

@@ -15,6 +15,10 @@
 
 namespace nt {
 
+/**
+ * Helper class for building Sendable dashboard representations for
+ * NetworkTables.
+ */
 class NTSendableBuilder : public wpi::SendableBuilder {
  public:
   /**

ntcore/src/main/native/include/networktables/Topic.h

@@ -396,6 +396,7 @@ class Publisher {
   Publisher() = default;
   explicit Publisher(NT_Publisher handle) : m_pubHandle{handle} {}
 
+  /// NetworkTables handle.
   NT_Publisher m_pubHandle{0};
 };