refactor: dir package [1]

[JeyJeyGao]

// The relative path to {NOTATION_CONFIG}
const (
    PathConfigFile  = "config.json"
    PathSigningKeys = "signingkeys.json"
    PathTrustPolicy = "trustpolicy.json"
)

func LocalKeyPath(name string) (keyPath, certPath string)
func X509TrustStoreDir(items... string) string

var (
    UserConfigDir    string // Aboslute path of user level {NOTATION_CONFIG}
    UserLibexecDir   string // Aboslute path of user level {NOTATION_LIBEXEC}
)

// ConfigFS and PluginFS can be an union fs
func ConfigFS() SysFS
func PluginFS() SysFS

type SysFS interface {
    fs.FS

    SysPath(items ...string) (string, error)
}
    func NewSysFS(root string) SysFS

Please review this PR before others.
Signed-off-by: Junjie Gao junjiegao@microsoft.com

[codecov-commenter]

Codecov Report

Merging #179 (3b373a0) into main (55b8746) will decrease coverage by 2.11%.
The diff coverage is 65.07%.

@@            Coverage Diff             @@
##             main     #179      +/-   ##
==========================================
- Coverage   82.37%   80.25%   -2.12%     
==========================================
  Files          23       22       -1     
  Lines        1821     1722      -99     
==========================================
- Hits         1500     1382     -118     
- Misses        254      266      +12     
- Partials       67       74       +7     

Impacted Files	Coverage Δ
config/base.go	55.00% <ø> (-18.92%)	⬇️
verification/verifier.go	83.41% <0.00%> (+0.43%)	⬆️
config/config.go	32.00% <40.00%> (-50.36%)	⬇️
config/keys.go	34.78% <40.00%> (-45.22%)	⬇️
verification/helpers.go	88.46% <62.50%> (-4.40%)	⬇️
dir/fs.go	66.66% <66.66%> (-11.12%)	⬇️
dir/path.go	88.88% <93.75%> (-3.42%)	⬇️
plugin/manager/manager.go	81.81% <100.00%> (ø)
verification/verifier_helpers.go	68.19% <100.00%> (ø)
... and 4 more

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[priteshbandi]

LGTM with one question

[shizhMSFT]

LGTM