fs: implement path separator info

dough-fs/src/commonMain/kotlin/gay/pizza/dough/fs/FsProvider.kt

@@ -2,5 +2,6 @@ package gay.pizza.dough.fs
 
 interface FsProvider : FsPathResolver {
   val currentWorkingDirectory: FsPath
+  val separator: String
   val operations: FsOperations
 }

dough-fs/src/jsMain/kotlin/gay/pizza/dough/fs/NodejsFsProvider.kt

@@ -1,8 +1,12 @@
 package gay.pizza.dough.fs
 
+import gay.pizza.dough.fs.nodefs.NodePathModule
+
 object NodejsFsProvider : FsProvider {
   override val currentWorkingDirectory: FsPath
     get() = NodePath(".")
+  override val separator: String
+    get() = NodePathModule.separator
 
   override val operations: FsOperations = NodeFsOperations
 

dough-fs/src/jsMain/kotlin/gay/pizza/dough/fs/nodefs/NodePathModule.kt

@@ -3,6 +3,9 @@ package gay.pizza.dough.fs.nodefs
 @JsModule("node:path")
 @JsNonModule
 external object NodePathModule {
+  @JsName("sep")
+  val separator: String
+
   @JsName("basename")
   fun baseName(path: String): String
 

dough-fs/src/jvmMain/kotlin/gay/pizza/dough/fs/JavaFsProvider.kt

@@ -6,6 +6,8 @@ import kotlin.io.path.absolute
 class JavaFsProvider(val fileSystem: FileSystem) : FsProvider {
   override val currentWorkingDirectory: FsPath
     get() = fileSystem.getPath(".").absolute().toFsPath()
+  override val separator: String
+    get() = fileSystem.separator
 
   override val operations: FsOperations = JavaFsOperations