Little FS improvements and IFS revisions to support user metadata

[mikee47]

Main changes

This PR adds the following methods to IFileSystem:

• setProfiler

This allows applications to hook into the low-level read/write/erase calls for debugging and profiling.

• fsetxattr
• fgetxattr
• setxattr
• getxattr

The setacl, settime, setattr and setcompression methods have been moved to FileSystem and
call the above new methods to do their work.

Additional overloads have been provided in FileSystem (and via methods of File objects):

• setAttribute
• getAttribute

These work with file handles or paths and have various convenient overloads.

• setUserAttribute, getUserAttribute

These are to access user-defined attributes.

For LFS volumes, each item is limited to a maximum size of 1023 bytes.

SPIFFS is less flexible (by design). Metadata is stored in the object headers
(after filename, etc.) and is restricted by the setting of SPIFFS_OBJ_META_LEN.
The first 16 bytes are used for system attributes (e.g. modified time), with user attributes
occupying any remaining space.

The current default setting (16) is unchanged, so if user metadata for SPIFFS volumes
is required then this must be increased accordingly.
Each user attribute requires a 2-byte header (tag + size).

• fopen
• fopendir

Removed - see below.

Fixes

• Revise HYFS to track file path

SPIFFS getFilePath() call sometimes returns weird results.

• Fix SPIFFS FileSystem::getFilePath return code

• Fix FileDir weirdness

The generic DirHandle type points to an IFS::FileDir struct, which each filesystem defines internally as required.
It looks like the compiler sometimes mixes these up and causes problems,
though this has only been seen when compiling in debug mode for Host.

So instead, redefine DirHandle as an abstract type, move the FileDir definition inside the appropriate filesystem namespace
and add the GET_FILEDIR() macro to deal with checking and casting.

• Fix memory leak in test module (thanks valgrind)

• Set lasterror in File::readContent()

• Fix FileSystem::makedirs()

• Fix LFS reported volumesize

Improvements

• Increase LFS_CACHE_SIZE from 16 to 32 bytes

Results in signficant reduction in read counts

• Switch to littlefs fork, manage file attributes manually

Only changed attributes (and those with non-default values) get written out
File time only gets updated if file is changed, opening in write mode is insufficient

• LFS mkdir sets mtime on success

• LFS mkdir succeeds if directory already exists

• Add LFS inspect sample

• Implement Host flush, rename and remove methods

• Helpers return FileSystem* instead of IFileSystem* for easier use

• Add optional IFileSystem::setProfiler method to enable flexible debugging and performance evaluation

• Revise hybrid filesystem to allow use of alternative writeable filesystem (e.g. Little FS)

• Remove IFileSystem.fopendir(Stat&) and IFileSystem.fopen(Stat&)

The goal of these methods was to provide more efficient means to open files/directories discovered during enumeration.
However, they are difficult to implement effectively and the additional complexity is hard to justify.

POSIX defines a whole raft of such methods such as openat, mkdirat, etc. which add an additional dirfd parameter
to specific the working directory. See https://man7.org/linux/man-pages/man3/open.3p.html for some background.

This may be re-visited in the future if the need arises.

• Add generic get/set attribute methods

These support LFS file/directory attributes as well as standard attribute types via AttributeTag.

There is no POSIX specification for this but the linux convention (setxattr, etc.) are appropriate.