Allow VFS picker clients to hide toolbar and context menus

[DeBaschdi]

Summary

Add optional picker UI controls for clients that need a focused selection workflow without maintaining local patches of the VFS toolkit.

• showToolbarActions: false hides built-in toolbar actions and custom picker buttons.
• showContextMenu: false hides context menus for files, folders, and the list background.
• The name filter and optional file-type filter remain available when toolbar actions are hidden.

Both options are available on:

• showSelectFilePicker
• showBrowseFilePicker
• showSaveFilePicker
• showDirectoryPicker

Example

const entries = await vfs.showSelectFilePicker({
  multiple: true,
  showToolbarActions: false,
  showContextMenu: false,
});