Add Bookmark and Note functionalities to PDF.js viewer

[execis]

Implementation Details

Bookmarks:

• Added a Bookmark button to the toolbar (viewer.html).
• Created a Bookmarks view in the sidebar to list all bookmarks (viewer.html, viewer.js).
• Implemented addBookmark and displayBookmarks methods in PDFViewerApplication (viewer.js).
• Updated PDFSidebar to handle the Bookmarks view (pdf_sidebar.js).

Notes:

• Added a Note button to the toolbar (viewer.html).
• Implemented addNote and displayNotesForPage methods in PDFViewerApplication (viewer.js).
• Notes are displayed on the pages where they were added and persist across sessions.

[Snuffleupagus]

Was this perhaps intended for a custom viewer implementation, since it's unfortunately not entirely clear here that this is functionality that belongs in the PDF.js repository itself?
(Also, based on a very brief look at the code this would likely require a fair bit of work before it could be considered.)

[execis]

Hey Jonas! Yes, I wanted to get started on it and hopefully get some feedback. The two buttons are now added to the top toolbar with some basic functionality but the details were not mentioned in the opened issue, so I'll see how functional I can make the two buttons.

[Snuffleupagus]

Before putting a bunch of work into this, please see #18865 (comment).