Annotation & XFA: Scale the font size in choicelist using zoom factor (bug 1715996)

- this is an accessibility issue which could be painful for some people with visual disabilities.

web/base_viewer.js

@@ -203,6 +203,8 @@ class BaseViewer {
       this.renderingQueue = options.renderingQueue;
     }
 
+    this._doc = document.documentElement;
+
     this.scroll = watchScroll(this.container, this._scrollUpdate.bind(this));
     this.presentationModeState = PresentationModeState.UNKNOWN;
     this._onBeforeDraw = this._onAfterDraw = null;
@@ -707,6 +709,8 @@ class BaseViewer {
       return;
     }
 
+    this._doc.style.setProperty("--zoom-factor", newScale);
+
     for (let i = 0, ii = this._pages.length; i < ii; i++) {
       this._pages[i].update(newScale);
     }

web/pdf_viewer.css

@@ -21,6 +21,7 @@
   --page-margin: 1px auto -8px;
   --page-border: 9px solid transparent;
   --spreadHorizontalWrapped-margin-LR: -3.5px;
+  --zoom-factor: 1;
 }
 
 @media screen and (forced-colors: active) {