Position annotation color popup near `mouseup` location

[dstillman]

https://forums.zotero.org/discussion/106834/position-the-color-selector-near-the-mouse-pointer-when-highlighting

Let's see how this feels.

[mrtcode]

https://forums.zotero.org/discussion/109552/zotero-7-annotation-comment-appears-off-of-screen-in-2-column-pdf https://forums.zotero.org/discussion/113387/zotero-pdf-reader-highlight-popup-location

Inter-page selection: https://forums.zotero.org/discussion/113777/zotero-7-beta-highlight-colors-popup-location-for-text-selection-across-2-pages#latest