Allow access to the PWM channel assigned to the Pin. Opportunity to change PWM configurations

[VasilyRakche]

Description of Change

In current code, after calling analogWrite(), pin is automatically assigned a channel. It is also configured. But:

• There is no way to change the channel configurations since one does not have access to the channel assigned to the pin - arduino-esp32/cores/esp32/esp32-hal-ledc.c:212
• Of course one can just use bare ledc functions, but there is no way to make it compatible with analogWrite(). If user calls the analogWrite() until it reaches the channel limit, original ledc configuration will be overwritten

Example. Better compatibility between ledc and native Arduino

#define PIN 20

// simple usage
analogWrite(PIN, 0);

// advanced user configuration update
channel = analogGetChannel(PIN);
int new_freq = 20000;
int new_bit_num = 9;
ledcSetup(channel, new_freq, new_bit_num);  

[P-R-O-C-H-Y]

Thanks @VasilyRakche for the PR, seems reasonable to have this option availible :)
Just fix the 1 comment I have, else its good and we can merge 👍

[PilnyTomas]

LGTM