It fixes#18849.
When such an annotation is deleted, we make sure that there are some data
to restore.
The version of this patch was making undoing a svg deletion buggy, so it's fixed now and
an integration test has been added for this case.
Given the following excerpt from the [Wikipedia article](https://en.wikipedia.org/wiki/Gill_Sans), mapping this to Helvetica should hopefully be fine:
> It has been described as "the British Helvetica" because of its lasting popularity in British design.
Given that the `WorkerTransport`-constructor will access all possible factory-instances, let's ensure that the `transportFactory`-object always has a consistent shape regardless of other options.
Also, since `useWorkerFetch` is always true in MOZCENTRAL builds we never need to create `CMapReaderFactory`/`StandardFontDataFactory`-instances there.
This unifies the various factory-options, since it's consistent with `CMapReaderFactory`/`StandardFontDataFactory`, and ensures that any needed parameters will always be consistently provided when creating `CanvasFactory`/`FilterFactory`-instances.
As shown in the modified example this may simplify some custom implementations, since we now provide the ability to access the `CanvasFactory`-instance used with a particular `getDocument`-invocation.
This code is quite old and has been moved/re-factored a few times over the years, however we can simplify this even further since we don't actually need a function to determine what NetworkStream-implementation to use.
Note that the textContent is returned in "chunks" from the API, through the use of `ReadableStream`s, and on the main-thread we're (normally) using just one temporary canvas in order to measure the size of the textLayer `span`s; see the [`#layout`](5b4c2fe1a8/src/display/text_layer.js (L396-L428)) method.
*Order of events, for parallel textLayer rendering:*
1. Call [`render`](5b4c2fe1a8/src/display/text_layer.js (L155-L177)) of the textLayer for page A.
2. Immediately call `render` of the textLayer for page B.
3. The first text-chunk for pageA arrives, and it's parsed/layout which means updating the cached [fontSize/fontFamily](5b4c2fe1a8/src/display/text_layer.js (L409-L413)) for the textLayer of page A.
4. The first text-chunk for pageB arrives, which means updating the cached fontSize/fontFamily *for the textLayer of page B* since this data is unique to each `TextLayer`-instance.
5. The second text-chunk for pageA arrives, and we don't update the canvas-font since the cached fontSize/fontFamily still apply from step 3 above.
Where this potentially breaks down is between the last steps, since we're using just one temporary canvas for all measurements but have *individual* fontSize/fontFamily caches for each textLayer.
Hence it's possible that the canvas-font has actually changed, despite the cached values suggesting otherwise, and to address this we instead cache the fontSize/fontFamily globally through a new (static) helper method.
*Note:* Includes a basic unit-test, using dummy text-content, which fails on `master` and passes with this patch.
Finally, pun intended, ensure that temporary textLayer-data is cleared *before* the `render`-promise resolves to avoid any intermittent problems in the unit-tests.
The idea is to insert a span in the text layer with an aria-role set to img
and use the bounding box provided by the attribute field in the tag dict in
order to have non-null dimensions for the image to make it "visible".
It has been tested with Voice Over (mac) and with NVDA (windows).
When an added stamp annotation is focused, the screen reader will announce
that it's a figure containing a graphic with the added alt-text.
The `Headers` functionality is now available in all browsers/environments that we support, which allows us to consolidate and simplify how the `httpHeaders` API-option is handled; see https://developer.mozilla.org/en-US/docs/Web/API/Headers#browser_compatibility
Also, simplifies the old `NetworkManager`-constructor a little bit.
