Fix Adafruit_GFX writeColor implementation for ESP32

[mikee47]

Fixes #2711

The problem occurs with a code path for ESP32 which buffers up to 32 pixels at a time for transfer. However, the first call to 'writePixels' clears the buffer to black (0 - empty response data). If the fill colour is black no abnormal operation is observed, but any other colour and at most 32 pixels get filled with the requested colour.

The benefit of these opimisations is minimal so the library is patched to simplify code path for all architectures.

[what-the-diff]

PR Summary

• Introduction of bigEndian variable
  The newly implemented variable bigEndian was created to handle specific tasks efficiently and ensure the system operates seamlessly.

• Modification of bigEndian related code
  The existing code related to the bigEndian variable has been also adjusted. This ensures that the whole system can fully utilize the potential benefits of this new variable and offer consistent performance.

• Addition of writeColor function
  A new function named writeColor was introduced. This new feature improves the system's color handling capabilities, providing a richer and more diverse visual experience for the users.

• Miscellaneous code modifications and deletions
  Routine maintenance tasks have been carried out with some minor code modifications and deletions done to enhance the overall code quality and maintainability. Although these are mainly minor tweaks, they might result in smoother operations and easier future updates.