Defer calling begin() on digital buses

NeoPixelBus requires that all parallel I2S bus members be constructed
before any of them call Begin().  Implement this by deferring the
call to the end of bus construction.

Fixes #4301.

wled00/bus_manager.h

@@ -79,6 +79,7 @@ class Bus {
 
     virtual ~Bus() {} //throw the bus under the bus
 
+    virtual void     begin() {};
     virtual void     show() = 0;
     virtual bool     canShow() const                          { return true; }
     virtual void     setStatusPixel(uint32_t c)                {}
@@ -213,7 +214,7 @@ class BusDigital : public Bus {
     uint16_t getLEDCurrent() const override  { return _milliAmpsPerLed; }
     uint16_t getUsedCurrent() const override { return _milliAmpsTotal; }
     uint16_t getMaxCurrent() const override  { return _milliAmpsMax; }
-    void reinit();
+    void begin() override;
     void cleanup();
 
     static std::vector<LEDType> getLEDTypes();