assets.json stores assets of all apps, so doesn't make sense to put it in frappe folder

Command:
node esbuild --files frappe/desk.bundle.js

Update only changed keys in assets.json instead of overwriting

- Add --apps option
- Add --production option
- Add --apps option for bench watch command
- Add --skip_frappe in esbuild

When you run build for specific apps, it should remove the entries of other apps

- Update assets_json directly from node
- Show error overlay or success message
- Open file in editor from error overlay

- For better HTTP caching and cache busting
- assets.json is created under [app]/dist folder which contains the map
of input file and output file name, this is used to get the correct path for
bundled assets

- basic watch mode
- Node paths include all app node_modules and app folders
- rename output directory to "dist"
- output files in flat directories: dist/js and dist/css

- add support for multiple file types

- Deprecate use of build.json
- *.bundle.js files placed anywhere in the public folder are bundled
- Built files are created in public/build folder which is gitignored

WIP