[CST816] Add support for Hynitron Microelectronics CST826 capacitive touch

[lboue]

What does this implement/fix?

Add support for Hynitron Microelectronics CST826 capacitive touch:

• CST826 Data sheet. High performance self-capacitance touch chip

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Other

Related issue or feature (if applicable): fixes #2715

Pull request in esphome-docs with documentation (if applicable): esphome/esphome-docs#3831

Test Environment

Adafruit Qualia ESP32-S3 :

• ESP32
• ESP32 IDF
• ESP8266
• RP2040
• BK72xx
• RTL87xx

Example entry for config.yaml:

touchscreen:
  platform: cst816
  id: my_touchscreen
  interrupt_pin: GPIO3
  reset_pin: GPIO21

Checklist:

• The code change is tested and works locally.
• Tests have been added to verify that the new code works (under tests/ folder).

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in esphome-docs.

[probot-esphome]

Hey there @clydebarrow, mind taking a look at this pull request as it has been labeled with an integration (cst816) you are listed as a code owner for? Thanks!
_{^{(message by CodeOwnersMention)}}