Support U[S]ART Inversion on STM32U0

[ndoo]

STM32U0 (and possibly other parts) support level inversion with the following:

huartx.AdvancedInit.AdvFeatureInit = UART_ADVFEATURE_TXINVERT_INIT;
huartx.AdvancedInit.TxPinLevelInvert = UART_ADVFEATURE_TXINV_ENABLE;

Please support these through the Arduino core.

Alternative workarounds include inverting the content before sending, or using an inverting buffer, but supporting this natively would be preferable.

Additional context

This is to support SDI-12 using the single-pin mode of the USART.

[fpistm]

Hi @ndoo
this issue is a duplicate of #1160 and already reference in #1418.
Feel free to contribute, for example UART Tx Rx pin swap function was added by a contributor in #2601.

[ndoo]

Hi @fpistm, thanks for capturing it on the list.

For now my plan is to add the inversion in hardware as I'm also adding a level shifter to 5V, but if I find some time I will take a look at #2601.