* Add VFS to enable POSIX file I/O operations
Enables use of FILE * operations on internal and external storage. fopen,
fclose, fseek, fprintf, fscanf, etc. supported.
* Add FS/File::stat and support POSIX stat/fstat
Removed FS::info64, and updates FS::info with the 64-bit version since in
2024 it's almost impossible to get a SD card smaller than 4GB.
Most code can simply replace info64 with info and continue operation, if they
were updated to be 64-bit in the first place.
Previously, File::readString used a C-style string as an intermediate
buffer via the String += operator. This treats a NUL byte as a
terminator, making this function work incorrectly if the File contains
binary data.
This commit switches the function to use String::concat, which doesn't
treat NUL bytes any differently (and is a bit faster, because it doesn't
need to use strlen).
