Move the various DOM-factories into their own files

- Over time the number and size of these factories have increased, especially the `DOMFilterFactory` class, and this split should thus aid readability/maintainability of the code.

 - By introducing a couple of new import maps we can avoid bundling the `DOMCMapReaderFactory`/`DOMStandardFontDataFactory` classes in the Firefox PDF Viewer, since they are dead code there given that worker-thread fetching is always being used.

 - This patch has been successfully tested, by running `$ ./mach test toolkit/components/pdfjs/`, in a local Firefox artifact-build.

*Note:* This patch reduces the size of the `gulp mozcentral` output by `1.3` kilo-bytes, which isn't a lot but still cannot hurt.

web/viewer-geckoview.html

@@ -59,6 +59,8 @@ See https://github.com/adobe-type-tools/cmap-resources
           "fluent-dom": "../node_modules/@fluent/dom/esm/index.js",
           "cached-iterable": "../node_modules/cached-iterable/src/index.mjs",
 
+          "display-cmap_reader_factory": "../src/display/cmap_reader_factory.js",
+          "display-standard_fontdata_factory": "../src/display/standard_fontdata_factory.js",
           "display-fetch_stream": "../src/display/fetch_stream.js",
           "display-network": "../src/display/network.js",
           "display-node_stream": "../src/display/stubs.js",

web/viewer.html

@@ -62,6 +62,8 @@ See https://github.com/adobe-type-tools/cmap-resources
           "fluent-dom": "../node_modules/@fluent/dom/esm/index.js",
           "cached-iterable": "../node_modules/cached-iterable/src/index.mjs",
 
+          "display-cmap_reader_factory": "../src/display/cmap_reader_factory.js",
+          "display-standard_fontdata_factory": "../src/display/standard_fontdata_factory.js",
           "display-fetch_stream": "../src/display/fetch_stream.js",
           "display-network": "../src/display/network.js",
           "display-node_stream": "../src/display/stubs.js",