Doxygen: SoA Get[Real/Int]Data (#3439)

## Summary

There are subtle differences with respect to access to runtime-added SoA
attributes in the overloads of these functions - adding a doc string as
in pyAMReX to clarify for users.

## Additional background

## Checklist

The proposed changes:
- [ ] fix a bug or incorrect behavior in AMReX
- [ ] add new capabilities to AMReX
- [ ] changes answers in the test suite to more than roundoff level
- [ ] are likely to significantly affect the results of downstream AMReX
users
- [x] include documentation in the code and/or rst files, if appropriate

Src/Particle/AMReX_StructOfArrays.H

@@ -31,9 +31,15 @@ struct StructOfArrays {
  [[nodiscard]] std::array<RealVector, NReal>& GetRealData () { return m_rdata; }
  [[nodiscard]] std::array< IntVector, NInt>& GetIntData () { return m_idata; }
 
+ /** Get access to the particle Real Arrays (only compile-time components) */
  [[nodiscard]] const std::array<RealVector, NReal>& GetRealData () const { return m_rdata; }
+ /** Get access to the particle Int Arrays (only compile-time components) */
  [[nodiscard]] const std::array< IntVector, NInt>& GetIntData () const { return m_idata; }
 
+ /** Get access to a particle Real component Array (compile-time and runtime component)
+ *
+ * @param index component with 0...NReal-1 compile-time and NReal... runtime arguments
+ */
  [[nodiscard]] RealVector& GetRealData (const int index) {
  AMREX_ASSERT(index >= 0 && index < NReal + static_cast<int>(m_runtime_rdata.size()));
  if (index >= 0 && index < NReal) return m_rdata[index];
@@ -43,6 +49,10 @@ struct StructOfArrays {
  }
  }
 
+ /** Get access to a particle Real component Array (compile-time and runtime component)
+ *
+ * @param index component with 0...NReal-1 compile-time and NReal... runtime arguments
+ */
  [[nodiscard]] const RealVector& GetRealData (const int index) const {
  AMREX_ASSERT(index >= 0 && index < NReal + static_cast<int>(m_runtime_rdata.size()));
  if (index >= 0 && index < NReal) return m_rdata[index];
@@ -52,6 +62,10 @@ struct StructOfArrays {
  }
  }
 
+ /** Get access to a particle Int component Array (compile-time and runtime component)
+ *
+ * @param index component with 0...NInt-1 compile-time and NInt... runtime arguments
+ */
  [[nodiscard]] IntVector& GetIntData (const int index) {
  AMREX_ASSERT(index >= 0 && index < NInt + static_cast<int>(m_runtime_idata.size()));
  if (index >= 0 && index < NInt) return m_idata[index];
@@ -61,7 +75,12 @@ struct StructOfArrays {
  }
  }
 
- [[nodiscard]] const IntVector& GetIntData (const int index) const {
+ /** Get access to a particle Int component Array (compile-time and runtime component)
+ *
+ * @param index component with 0...NInt-1 compile-time and NInt... runtime arguments
+ * @return
+ */
+ [[nodiscard]] const IntVector& GetIntData (const int index) const {
  AMREX_ASSERT(index >= 0 && index < NInt + static_cast<int>(m_runtime_idata.size()));
  if (index >= 0 && index < NInt) return m_idata[index];
  else {