[editor] Support disabling of editing when pdfjs.enablePermissions is set (issue 15049)

For encrypted PDF documents without the required permissions set, this patch adds support for disabling of Annotation-editing. However, please note that it also requires that the `pdfjs.enablePermissions` preference is set to `true` (since PDF document permissions could be seen as user hostile).[1]

As I started looking at the issue, it soon became clear that *only* trying to fix the issue without slightly re-factor the surrounding code would be somewhat difficult.
The following is an overview of the changes in this patch; sorry about the size/scope of this!

 - Use a new `AnnotationEditorUIManager`-instance *for each* PDF document opened in the GENERIC viewer, to prevent user-added Annotations from "leaking" from one document into the next.

 - Re-factor the `BaseViewer.#initializePermissions`-method, to simplify handling of temporarily disabled modes (e.g. for both Annotation-rendering and Annotation-editing).

 - When editing is enabled, let the Editor-buttons be `disabled` until the document has loaded. This way we avoid the buttons becoming clickable temporarily, for PDF documents that use permissions.

 - Slightly re-factor how the Editor-buttons are shown/hidden in the viewer, and reset the toolbar-state when a new PDF document is opened.

 - Flip the order of the Editor-buttons and the pre-exising toolbarButtons in the "toolbarViewerRight"-div. (To help reduce the size, a little bit, for the PR that adds new Editor-toolbars.)

 - Enable editing by default in the development viewer, i.e. `gulp server`, since having to (repeatedly) do that manually becomes annoying after a while.

 - Finally, support disabling of editing when `pdfjs.enablePermissions` is set; fixes issue 15049.

---

[1] Either manually with `about:config`, or using e.g. a [Group Policy](https://github.com/mozilla/policy-templates).

web/viewer.js

@@ -93,7 +93,6 @@ function getViewerConfiguration() {
           ? document.getElementById("openFile")
           : null,
       print: document.getElementById("print"),
-      editorModeButtons: document.getElementById("editorModeButtons"),
       editorNoneButton: document.getElementById("editorNone"),
       editorFreeTextButton: document.getElementById("editorFreeText"),
       editorInkButton: document.getElementById("editorInk"),