Use -Oz instead of -O2 to reduce compiled asset sizes significantly (#479)

* Run `npm ci` automatically after the devcontainer is created.
This reduces the chance that another dev will forget to do this.

* Upgrade to Emscripten 2.0.29
Changes required:
* Defined EM_NODE_JS environment variable to get rid of
a warning that appears if the NODE environment variable
is set, but EM_NODE_JS is not.
* EXTRA_EXPORTED_RUNTIME_METHODS is now EXPORTED_RUNTIME_METHODS
* No longer pass the `-s LINKABLE=1` option to emcc when compiling. (This is a linktime setting and emcc
warns about not using a linktime setting when compiling now).

* Upgrade to Sqlite 3.36.0
Sqlite now publishes the hash as a SHA3 instead of SHA1,
necessitating the installation of the sha3sum command.

* Use -Oz optimizations instead of -O2
This reduces most compilation output by around 50%