Libraries updated to support new RP2040-based boards (RASPBERRY_PI_PICO, etc.)

Could you please update the SafeString Library to also support Earle Philhower's arduino-pico core.

The compile error:

In file included from /home/kh/Arduino/libraries/SafeString/examples/SafeString_Tests/SafeStringCaseChanges/SafeStringCaseChanges.ino:13:
/home/kh/Arduino/libraries/SafeString/src/SafeString.h:120:10: fatal error: Printable.h: No such file or directory
  120 | #include <Printable.h>
      |          ^~~~~~~~~~~~~
compilation terminated.
exit status 1
Error compiling for board Raspberry Pi Pico.