fs: adapt to different mkdir api, block write to root dir, add tests

[XiaochenCui]

• fix fs: failed to mkdir when parent arg is missing #1367
• adapt to different mkdir APIs
• add tests for create_missing_parents arg
• add tests for "mkdir in root directory"

test:

> node ./tools/api-tester/apitest.js --config=./tools/api-tester/config.yml --unit

=== Test Results ===
┌─────────────────────────────────┬────────┬────────┬───────┐
│ (index)                         │ passed │ failed │ total │
├─────────────────────────────────┼────────┼────────┼───────┤
│ Cartesian Test for /write       │ 24     │ 0      │ 24    │
│ Cartesian Test for /move        │ 44     │ 4      │ 48    │
│ Cartesian Test for /copy        │ 144    │ 0      │ 144   │
│ write and read                  │ 6      │ 0      │ 6     │
│ move                            │ 4      │ 0      │ 4     │
│ stat                            │ 133    │ 1      │ 134   │
│ readdir                         │ 115    │ 0      │ 115   │
│ mkdir                           │ 22     │ 0      │ 22    │
│ batch                           │ 4      │ 0      │ 4     │
│ delete                          │ 7      │ 0      │ 7     │
│ single write for trace and span │ 0      │ 0      │ 0     │
└─────────────────────────────────┴────────┴────────┴───────┘

All mkdir tests passed. The failed tests are unrelated to this PR.

[XiaochenCui]

@KernelDeimos
this PR is ready for review & merge