When XFA support was added, the size of the *built* `pdf.worker.js` file increased quite a bit. Hence I think that it makes sense to, where easily possible, do what we can to (slightly) reduce the size of the PDF.js library.
The supplemental font data files (added for XFA rendering), containing rescale-factors respectively widths, seem like an excellent candidate here since they're not particularly large in either line-count or file sizes.
In this patch these files are instead merged into a *single* file per font, rather than four different ones, and even with these changes the resulting source files don't become all that large.[1]
For e.g. the `gulp mozcentral` build, this reduces the size of the *built* `pdf.worker.js` file by more than `3 kB`. Given the overall simplicity of the patch, that kind of size decrease definitely seem worthwhile to me.
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[1] Especially when compared to truly large files such as e.g. `glyphlist.js`, `metrics.js`, and `unicode.js`.
- some pdf use some fonts which are not embedded or they don't have any width array or don't have any css info (e.g. for standard fonts or Arial).
- so add widths arrays for Liberation fonts in order to compute the ones for other fonts in using scale factors array.
- Some js files contain scale factors for each glyph in order to rescale Liberation to have a final font with the correct width.
- A lot of XFA have some containers where their dimensions are based on their text content, so using default font from browser can lead to an almost unreadable pdf.
