AP_HAL_ESP32: check UART thread ownership

[srmainwaring]

Add checks that UART driver functions are called on the thread the port is initialised on, and handle a change of thread ownership.

Motivation

• Fix an issue where calling UARTDriver::_begin with a baudrate of zero (for example when changing the thread owning the UART while initialising the AP_MSP_Telem_Backend) causes a core panic due to an integer division by zero exception.
• The implementation follows the equivalent AP_HAL_ChibiOS UART driver.

Testing

• Configure, build and flash esp32s3empty.
• Set SERIAL3_BAUD 115.
• Set SERIAL3_PROTOCOL 32.
• Without this change there is a core panic on the MSP thread.
• With this change a MSP GPS such as the Mateksys M8Q will work (set GPS1_TYPE = 19).

[tpwrules]

Looks right and was able to test that the crash is fixed though I don't have an MSP GPS.

This is another strange area of the code I'd like to fix, but for now ESP32 should better match ChibiOS.

[davidbuzz]

reviewed ok too