[api-minor] Improve pdf reading in high contrast mode

- Use Canvas & CanvasText color when they don't have their default value
  as background and foreground colors.
- The colors used to draw (stroke/fill) in a pdf are replaced by the bg/fg
  ones according to their luminance.

web/app_options.js

@@ -129,6 +129,16 @@ const defaultOptions = {
     compatibility: compatibilityParams.maxCanvasPixels,
     kind: OptionKind.VIEWER,
   },
+  pageBackgroundColor: {
+    /** @type {string} */
+    value: "Canvas",
+    kind: OptionKind.VIEWER + OptionKind.PREFERENCE,
+  },
+  pageForegroundColor: {
+    /** @type {string} */
+    value: "CanvasText",
+    kind: OptionKind.VIEWER + OptionKind.PREFERENCE,
+  },
   pdfBugEnabled: {
     /** @type {boolean} */
     value: typeof PDFJSDev === "undefined" || !PDFJSDev.test("PRODUCTION"),