Add initial support for USB MSC (#5466)

* Add initial support for USB MSC

* Add Firmware Upload/Download With MSC

Current running firmware is available as file inside the MSC Disk. To update the firmware on the ESP, just copy a regular firmware bin into the drive

* Support overwriting of the firmware file

Overwriting a file is done totally differently on MacOS, Windows and Linux. This change supports it on all of them.

* Allow CDC, FirmwareMSC and DFU to be enabled on boot

* Add example ESP32-S2 USB-ONLY board

* Various device code optimizations

Added `end()` methods to MSC classes
Made begin() methods safe to be called multiple times
Optimized CDC class

* Fix CDC Connect/Disconnect detection in Arduino IDE on Windows

* Rework cdc_write

* Update ESP32-S2 board configs

libraries/USB/keywords.txt

@@ -8,6 +8,7 @@
 
 USB	KEYWORD1
 USBCDC	KEYWORD1
+USBMSC	KEYWORD1
 
 #######################################
 # Methods and Functions (KEYWORD2)
@@ -18,6 +19,14 @@ end	KEYWORD2
 onEvent	KEYWORD2
 enableReset	KEYWORD2
 
+vendorID	KEYWORD2
+productID	KEYWORD2
+productRevision	KEYWORD2
+mediaPresent	KEYWORD2
+onStartStop	KEYWORD2
+onRead	KEYWORD2
+onWrite	KEYWORD2
+
 #######################################
 # Constants (LITERAL1)
 #######################################