To avoid introducing any inline "hacks" in the viewer-code this meant adding `useSystemFonts` to the AppOptions, which thus required some new functionality since the default value should be `undefined` given how the option is handled in the API; note [this code](ed83d7c5e1/src/display/api.js (L298-L301)).
Finally, also moves the definition of the development-mode `window.isGECKOVIEW` property to the HTML file such that it's guaranteed to be set regardless of how and when it's accessed.
Given that only the GENERIC viewer supports opening more than one PDF document, we can simplify things a tiny bit by instead generating the necessary DOM-element in JavaScript.
This *special* build-target is very old, and was introduced with the first pre-processor that only uses comments to enable/disable code.
When the new pre-processor was added `PRODUCTION` effectively became redundant, at least in JavaScript code, since `typeof PDFJSDev === "undefined"` checks now do the same thing.
This patch proposes that we remove `PRODUCTION` from the JavaScript code, since that simplifies the conditions and thus improves readability in many cases.
*Please note:* There's not, nor has there ever been, any gulp-task that set `PRODUCTION = false` during building.
To make this functionality work out-of-the-box in custom implementations, see e.g. the "viewer components" examples, it'd be slightly easier if we dynamically create/insert the "hiddenCopyElement" in the `PDFViewer` constructor.
Given that the "copy all text" feature still appears to work just as before with this patch, hopefully I'm not overlooking any reason why doing this would be a bad idea.
This further extends the web-specific import maps introduced in PR 16009, to allow removing *most* of the build-time `require` statements from the viewer. The few remaining ones are fallbacks used for the COMPONENTS respectively the `legacy` GENERIC builds.
After the compatibility updates in PR 15968 it's no longer strictly necessary to build the `viewer.css` file in order for the *development viewer* to work in Chromium-based browsers.
*Please note:* Given that Chromium-based browsers still don't support the *unprefixed* `mask-image` property the icons won't look right, however the development viewer itself works.
Given that Firefox is the *primary* development target, and that running `gulp generic` locally will generate polyfilled CSS, it seems reasonable to make this simplification here.
Currently we have a couple of pre-processor checks, specifically for the GV-viewer, spread throughout the code. This works fine when *building* the viewer, however they're obviously ignored in development mode (i.e. `gulp server`).
This leads to a situation where the GV development viewer, i.e. http://localhost:8888/web/viewer-geckoview.html, behaves subtly different from its built version. This could easily lead to bugs, hence this patch introduces a development mode constant to hopefully improve things here.
Finally, in a follow-up to PR 15842, also ignores the `pageMode`-state since there's no sidebar available.
