Support higher modulation frequencies and better precision

[zehnm]

Cherry-picking the PWM improvements from upstream's PR: crankyoldgit#2074

Uses fixed point pulse widths for higher precision and polling of micros instead of delay to be able to reach the frequencies required.
On ESP8266 lower than 160 MHz a free running PWM mode was also added to get as close to 455 kHz as possible.
A bonus is that the lower frequencies now are accurate to within a few hertz.

Verified with a logic analyzer on the GPIO pin. Signal definitely looks cleaner on this ESP32-S3 ESP-IDF implementation.