Improvements for -S2

- new partition table for boards with UF2 boot (Adafruit qt py S2)
- better treatment of debug out using "USBCDC" native port
- workarounds for watchdog crashes on -S2
- Add missing but mandatory build flags for -S2 and -C3

tools/partitions-4MB-tinyuf2_spiffs.csv

@@ -0,0 +1,11 @@
+# ESP-IDF Partition Table
+# Name,   Type, SubType, Offset,  Size, Flags
+# bootloader.bin,,          0x1000, 32K
+# partition table,          0x8000, 4K
+
+nvs,      data, nvs,      0x9000,  20K,
+otadata,  data, ota,      0xe000,  8K,
+ota_0,    0,    ota_0,   0x10000,  1408K,
+ota_1,    0,    ota_1,  0x170000,  1408K,
+uf2,      app,  factory,0x2d0000,  256K,
+spiffs,   data, spiffs, 0x310000,  960K,