Support new "Sig" type in pdfjs

[Jefiozie]

Before you start - checklist

• I understand that React-PDF does not aim to be a fully-fledged PDF viewer and is only a tool to make one
• I have checked if this feature request is not already reported

Is your feature request related to a problem? Please describe.

Describe what the problem is. Ex. I'd like to do […] with my PDFs.

At the moment the library doesn't support the new "Sig" widget.

Describe the solution you'd like

What you want to happen?

To support the new widget the pdfjs core lib from Mozilla should be update to the latest release. This version is now supporting this new type Pdfjs 13214

[wojtekmaj]

Related to #772
Related to #691
Related to #559

[wojtekmaj]

Please kindly check v5.4.0-beta.2 in which support for Sig type has been added.

[Jefiozie]

@wojtekmaj , I just verified that indeed it works with the latest beta versions