feature/shared requirements txt parser

[whitphx]

• Create @stlite/common private package that contains shared code: Resolves Create @stlite/common or @stlite/utils package #431
• Update the requirements.txt parser to ignore commented lines: Resolves Improve the requirements.txt parser to ignore comment lines #430
• Introduce a bundler (esbuild) to build desktop/bin/*.js to embed the code from the common package. See the comment below for the details.

[whitphx]

• Introduce a bundler to embed the code from @stlite/common, which is a private package, into bin/dump_artifacts.js.
• We selected esbuild as the bundler because it supports everything needed out-of-the-box such as TypeScript it just worked with simple configs.
  • Webpack v4 does not support some necessary features such as handling import.meta.url and does things too much such as injecting their original require implementation which leads to unavailability of require.resolve.
  • Rollup.js does not work well at bundling @stlite/common even if we converted it to be a CommonJS module or introduced node-resolve and commonjs plugins.