Component model for filesystem access

[Loara]

Component model can be used to introduce a more granular control on filesystem access for wasm applications, and by converse improve the interoperability between wasi packages.

A filesystem interface is just a plain text file containing a list of relative paths and permissions. A simple MyInterface filesystem interface file can contain the following lines:

path1/file1 r
path1/path2/file2 rw
file3 re

Such interface can be later imported by a wasm interpreter with a --import-file-interface command line option containing both the filesystem interface name and an absolute path containing all the files specified in the interface

--import-file-interface My interface /some/abs/path/dir/

It could be a useful feature to enable a finer way to control filesystem access.