Set up (optional) devcontainer for browser-based contributions

[StevenClontz]

Recreated from sean-fitzpatrick#37 which has some additional discussion

This change will support Codespace users out of the box. I just used it to successfully (by a spot check at least) build and preview the HTML target, which took no more than one hour:

Follow-up builds wouldn't need to recreate the asymptote or latex-image assets, so I would recommend regular users to set this codespace to never expire (keeping in mind you can only do this with so many codespaces before you run out of free resources). I'm about to edit the README to reflect my recommendations and then mark this ready for review.

[APEXCalculus]

Let's give this a go. Don't fully understand the changes made, but I'd love to be able to edit things in the browser.

[APEXCalculus]

Not sure if this is a @StevenClontz or an @sean-fitzpatrick issue.
Got a Codespace built and was able to run `pretex build latex-novideo'. (Good!)
It created a lot of generated-assets. (Good!)
I got a TeX-able file. (Good! - though I still need to download the image files.)

There were error messages during that build. It seems there was trouble with Asymptote? Some of the log:

QR code creation complete
converting Asymptote diagrams from /workspaces/APEXCalculusPTX/ptx/apex.ptx to PDF graphics for placement in /workspaces/APEXCalculusPTX/generated-assets/asymptote with method "AsyMethod.LOCAL"
extracting Asymptote diagrams from /workspaces/APEXCalculusPTX/ptx/apex.ptx
XSL conversion of /workspaces/APEXCalculusPTX/ptx/apex.ptx by /root/.ptx/2.42.0/core/xsl/extract-asymptote.xsl
successful application of /root/.ptx/2.42.0/core/xsl/extract-asymptote.xsl
converting /ptx-b8d44jrj/img_disk1a_3D.asy to /ptx-b8d44jrj/img_disk1a_3D.pdf
warning: the Asymptote output /ptx-b8d44jrj/img_disk1a_3D.pdf was not built
warning:              Perhaps your code has errors (try testing in the Asymptote web app).
warning:              Or your local copy of Asymtote may precede version 2.66 that we expect.
warning:              In this case, not every image can be built in every possible format.
warning: 
warning:              Your Asymptote reports its version within the following:
warning:              Asymptote version 3.09 [(C) 2004-26 Andy Hammerlindl, John C. Bowman, Tom Prince]
warning: 
warning: ENABLED OPTIONS:
warning: V3D      3D vector graphics output
warning: WebGL    3D HTML rendering
warning: OpenGL   3D OpenGL rendering
warning: SSBO     GLSL shader storage buffer objects
warning: Eigen    Eigenvalue library
warning: XDR      External Data Representation (portable binary file format for V3D)
warning: LSP      Language Server Protocol
warning: Readline Interactive history and editing
warning: GC       Boehm garbage collector
warning: threads  Render OpenGL in separate thread
warning: 
warning: DISABLED OPTIONS:
warning: GSL      GNU Scientific Library (special functions)
warning: FFTW3    Fast Fourier transforms
warning: CURL     URL support
warning: Sigsegv  Distinguish stack overflows from segmentation faults
error: Failed to generate asymptote diagram img_disk1a_3D.asy in pdf format.
error: Unable to generate some asymptote elements: 
error: Failed to generate asymptote diagram img_disk1a_3D.asy in pdf format.
Checking for update for required playwright chromium browser.
using playwright package to create previews for interactives from /workspaces/APEXCalculusPTX/ptx/apex.ptx for placement in /workspaces/APEXCalculusPTX/generated-assets/preview
XSL conversion of /workspaces/APEXCalculusPTX/ptx/apex.ptx by /root/.ptx/2.42.0/core/xsl/extract-interactive.xsl
successful application of /root/.ptx/2.42.0/core/xsl/extract-interactive.xsl
automatic screenshot of interactive with identifier "interactive-label" on page http://localhost:8888/interactive-label.html to file interactive-label-preview.png
Closing http.server thread
Removing temporary directory /ptx-7ksneyt4
Removing temporary directory /ptx-d7ptwd60
Removing temporary directory /ptx-b8d44jrj
Removing temporary directory /ptx-vbeaj7ex
Building with custom xsl /workspaces/APEXCalculusPTX/xsl/apex-latex-style.xsl
Preparing to build into /workspaces/APEXCalculusPTX/output/latex-novideo.
converting /workspaces/APEXCalculusPTX/ptx/apex.ptx to LaTeX as /ptx-10r_k85f/apex.tex
XSL conversion of /workspaces/APEXCalculusPTX/ptx/apex.ptx by /ptxcli_wdb1wr7t/cli_xsl/apex-latex-style.xsl
messages from the log for XSL processing:
* PTX:INFO:   checking all deprecated elements.
successful application of /ptxcli_wdb1wr7t/cli_xsl/apex-latex-style.xsl
Removing temporary directory /ptx-10r_k85f
Removing temporary directory /ptx-9ksiyo75
Removing temporary directory /ptx-ukzyo53g

Finished build for target latex-novideo. The output is in /workspaces/APEXCalculusPTX/output/latex-novideo.

critical: There were errors during the build.  See above.
------------------------
critical: Failed to build without errors.  Exiting...

----------------------------------------------------
While running pretext, the following errors occurred:

(see log messages above or in the 'logs' folder for more information)
error: Failed to generate asymptote diagram img_disk1a_3D.asy in pdf format.
error: Unable to generate some asymptote elements: 
error: Failed to generate asymptote diagram img_disk1a_3D.asy in pdf format.
critical: There were errors during the build.  See above.
critical: Failed to build without errors.  Exiting...