[FR] Provide multiple output formats to IJulia

[benz0li]

Currently, only one output format is provided: The first match of https://github.com/JuliaLang/IJulia.jl/blob/1cdaf7e5e65c1221b4a3fac86f63253bea65a0c5/src/display.jl#L19-L28 with what the backend provides.

Please provide every MIME type specified in the first level of that vector.
👉 After executing IJulia.register_mime(MIME("application/pdf")) I would like Plots.js (GR backend) to return both image/svg+xml and application/pdf.

This allows IJulia to use

• image/svg+xml for plot display in the browser
  + HTML conversion using SVG
• application/pdf for direct PDF conversion

---

See JuliaLang/IJulia.jl#771 on a similar discussion about DataFrames.jl.

[benz0li]

Cross references:

• Enable PDF Export in IJulia #4188
  • support for pdf plot output JuliaLang/IJulia.jl#1035
  • Fix PDF render JuliaLang/IJulia.jl#1038 (comment)
• [ENH] - Remove inkscape jupyter/docker-stacks#1754
  ℹ️ With application/pdf plot format in the notebook file, inkscape is not required for PDF conversion using nbconvert.
  • Removing inkscape package from the minimal-notebook jupyter/docker-stacks#1765

[benz0li]

See MakieOrg/Makie.jl#2195 (comment) for the discussion about vector graphics becoming very large and slow for plots with lots of data points.