Prepare for ESP32 WDT

[s-hadinger]

Description:

Prepare for ESP32 watchdog (WDT):

• enable with #define USE_ESP32_WDT (not enabled by default until after v14)
• calling yield() resets the watchdog, also now called with Berry tasmota.yield()
• modified yield() to call feedLoopWDT()

No functional change until USE_ESP32_WDT is enabled

Checklist:

• The pull request is done against the latest development branch
• Only relevant files were touched
• Only one feature/fix was added per PR and the code change compiles without warnings
• The code change is tested and works with Tasmota core ESP8266 V.2.7.6
• The code change is tested and works with Tasmota core ESP32 V.3.0.0
• I accept the CLA.

NOTE: The code change must pass CI tests. Your PR cannot be merged unless tests pass