Decode URL encoded filenames from content disposition headers

[wangsongyan]

pdf.js cannot correctly display urlencode contentDispositionFilename, so I add the decode logic of contentDispositionFilename in extractFilenameFromHeader.

[Snuffleupagus]

First of all, this needs a better and more readable commit message than just "support urlencode contentDispositionFilename", since it's a bit difficult to decipher when looking at only the commit message (e.g. at the git command line) and not the code itself.
Second of all, please make sure to follow https://github.com/mozilla/pdf.js/wiki/Squashing-Commits.

Edit: Looks like a replacement for PR #10381.

[timvandermeij]

/botio unittest

[pdfjsbot]

From: Bot.io (Linux m4)

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Received

Command cmd_unittest from @timvandermeij received. Current queue size: 0

Live output at: http://54.67.70.0:8877/fb59e1390fa69ef/output.txt

[pdfjsbot]

From: Bot.io (Windows)

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Received

Command cmd_unittest from @timvandermeij received. Current queue size: 0

Live output at: http://54.215.176.217:8877/598b77df2dd7ca6/output.txt

[pdfjsbot]

From: Bot.io (Linux m4)

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Success

Full output at http://54.67.70.0:8877/fb59e1390fa69ef/output.txt

Total script time: 2.67 mins

• Unit Tests: Passed

[pdfjsbot]

From: Bot.io (Windows)

---

Success

Full output at http://54.215.176.217:8877/598b77df2dd7ca6/output.txt

Total script time: 5.33 mins

• Unit Tests: Passed

[timvandermeij]

Thank you for improving this!