Add reset_filesystem

Author: jlongster

src/api.js

@@ -1277,4 +1277,9 @@ Module["onRuntimeInitialized"] = function onRuntimeInitialized() {
       let fileInfo = filesInfo.find(f => f[1] === path);
       sqliteFiles.delete(fileInfo[0])
     }
+
+    Module["reset_filesystem"] = () => {
+      FS.root = null;
+      FS.staticInit();
+    }
 };

src/fs-externs.js

@@ -5,10 +5,8 @@
 Module.FS = class {
   constructor() {
     this.ErrnoError = class {};
-    this.filesystems = {}
   }
   mount() {}
-  unmount() {}
   isRoot() {}
   isFile() {}
   isDir() {}