Bundle extension & add publish workflow

[Splines]

• Starting with this PR, we now bundle the extension with esbuild. This had some consequences in how tests are spun up (one annoyance is that the tests have to manually adjust the extension entry point in package.json since they can only be served from another folder).
• We also add a publish workflow, such that we can finally publish the first version of this extension ;)

Off-topic:

• Improved the regex for the logger to find method names in more cases (aside from file names).