Add output tags to all JavaScript source files

[omarreiss]

To make it clear where a JavaScript file in source is built to, I'm adding @output tags to all JavaScript files that are not vendor scripts.

@herregroen is working on a patch to parse these to automatically generate entry tags for Webpack.

The plan is to create a JSDoc plugin to parse those for Devhub as well.

[omarreiss]

Fixed 1 typo

[omarreiss]

Had to rebase...

[omarreiss]

Makes sure single line comments become multiline

[atimmer]

In 43347:

Docs: Add file doc @output annotations.

These annotations make it clear to the reader of a JavaScript source
where the build process outputs to. These annotations can later be
integrated in a webpack configuration. This way there is one source of
truth.

The build folder is omitted from the paths, because a single JS file
shouldn't not be responsible of knowing where outputs in general will
end up at. A file only knows its output location relative to the
project.

Props adamsilverstein, herregroen, omarreiss, pento.
Fixes #44361.