Disable link annotations during text selection

When selecting text, hovering over an element
causes all the text between (according the the dom
order) the current selection and that element to
be selected.

This means that when, while selecting, the cursor
moves over a link, all the text in the page gets
selected. Setting `user-select: none` on the link
annotations would improve the situation, but it
still makes it impossible to extend the selection
within a link without using Shift+arrows keys on
the keyboard.

This commit fixes the problem by setting
`pointer-events: none` on the `<section>`s in the
annotation layer while selecting some text. This
way, they are ignored for hit-testing and do not
affect selection.

It is still impossible to _start_ a selection
inside a link, as the link text is covered by the
link annotation.

Fixes #18266

web/annotation_layer_builder.css

@@ -126,6 +126,10 @@
     }
   }
 
+  .textLayer.selecting ~ & section {
+    pointer-events: none;
+  }
+
   :is(.linkAnnotation, .buttonWidgetAnnotation.pushButton) > a {
     position: absolute;
     font-size: 1em;

web/text_layer_builder.css

@@ -118,9 +118,9 @@
     z-index: 0;
     cursor: default;
     user-select: none;
+  }
 
-    &.active {
-      top: 0;
-    }
+  &.selecting .endOfContent {
+    top: 0;
   }
 }

web/text_layer_builder.js

@@ -150,8 +150,8 @@ class TextLayerBuilder {
   #bindMouse(end) {
     const { div } = this;
 
-    div.addEventListener("mousedown", evt => {
-      end.classList.add("active");
+    div.addEventListener("mousedown", () => {
+      div.classList.add("selecting");
     });
 
     div.addEventListener("copy", event => {
@@ -193,16 +193,42 @@ class TextLayerBuilder {
         end.style.width = "";
         end.style.height = "";
       }
-      end.classList.remove("active");
+      textLayer.classList.remove("selecting");
     };
 
+    let isPointerDown = false;
+    document.addEventListener(
+      "pointerdown",
+      () => {
+        isPointerDown = true;
+      },
+      { signal }
+    );
     document.addEventListener(
       "pointerup",
       () => {
+        isPointerDown = false;
         this.#textLayers.forEach(reset);
       },
       { signal }
     );
+    window.addEventListener(
+      "blur",
+      () => {
+        isPointerDown = false;
+        this.#textLayers.forEach(reset);
+      },
+      { signal }
+    );
+    document.addEventListener(
+      "keyup",
+      () => {
+        if (!isPointerDown) {
+          this.#textLayers.forEach(reset);
+        }
+      },
+      { signal }
+    );
 
     if (typeof PDFJSDev === "undefined" || !PDFJSDev.test("MOZCENTRAL")) {
       // eslint-disable-next-line no-var
@@ -237,7 +263,7 @@ class TextLayerBuilder {
 
         for (const [textLayerDiv, endDiv] of this.#textLayers) {
           if (activeTextLayers.has(textLayerDiv)) {
-            endDiv.classList.add("active");
+            textLayerDiv.classList.add("selecting");
           } else {
             reset(endDiv, textLayerDiv);
           }