Add screen flip function for ST7789

[zivyuan]

Screen flip function was useful in some applications that use mirrors.

Add flip flag added to setRotation() function.

void setRotation(uint8_t r, bool flip);

Only tested on 1.3" TFT screen with 7 pins.

[meithon]

This program was worked in a ST7789 1.14inch(135*140px) display perfectly.
you was helpful becouse have make this. thanks :).

[jbry]

Found this because I was using this:
https://docs.espressif.com/projects/esp-idf/en/latest/esp32s2/hw-reference/esp32s2/user-guide-esp-lyrap-lcd32-v1.1.html
and everything was mirrored. I know this PR is old - but wanted to express my thanks as it got me out of a hole :)

[baptistereb]

Hi, any news ? Because I've also troubles with my screen and it should help

[tamsanh]

@zivyuan Thanks for this! I was banging my head against some sample ESP32 code I found that was drawing on a TFT that used this library. I was able to copy your fixed class into my code as a standalone new class, and it saved me. Thanks so much!

[ladyada]

instead of changing setRotation, which is used in like every other TFT library we maintain, please rename/adapt to a new function void flip(bool);