machine/esp32: add PWM support using LEDC peripheral

Add PWM support for ESP32 using the LEDC (LED Control) peripheral.

Features:
- 4 high-speed timers (PWM0-PWM3) with glitch-free duty updates
- Up to 8 channels shared across timers
- Configurable duty resolution (1-20 bits)
- Flexible frequency control via period setting
- Any GPIO can be used via GPIO matrix routing

The implementation follows the standard TinyGo PWM interface with
Configure, Channel, Set, SetPeriod, Top, and SetInverting methods.

Co-authored-by: Ona <no-reply@ona.com>

Author: jespino

src/examples/pwm/esp32.go

@@ -0,0 +1,12 @@
+//go:build esp32
+// +build esp32
+
+package main
+
+import "machine"
+
+var (
+	pwm  = machine.PWM0  // Use high-speed timer 0
+	pinA = machine.GPIO2 // Built-in LED on many ESP32 boards
+	pinB = machine.GPIO4 // Another GPIO for testing
+)