Return ENotCapable error when accessing unknown files on root (for #3263 and #3264)

[ptitSeb]

Fixes for wasm.fyi tests:

• When accessing bad path from the root, return ENOTCAPABLE error instead of ENOENT (root can only contains pre-openned folder, no other capability)
• Accessing ROOT for other things then entering folder should result in ENOTCAPABLE

[syrusakbary]

We need to add also a test

[ptitSeb]

We need to add also a test

This is a challenge here: the original tests are based on C code and around specific syscall error code return or Exit Code value. There is no infrastructure to do that on wasmer tests
Like:

With a mapdir test_fs run

#include <assert.h>
#include <errno.h>
#include <stdio.h>

int main() {
  FILE* file = fopen("test_fs.not/..", "r");
  assert(file == NULL);
  assert(errno == ENOTCAPABLE);

  return 0;
}

or simply run

#include <stdlib.h>

int main(void) {
    abort();

    return 0;
}

And check that the exit code is 134 (128+SIGABRT) on linux-like env. (or 3 on windows)

[ptitSeb]

bors r+

[bors]

Build succeeded:

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