perf: remove comments from js-files

[csvn]

Description:

Strip comments from all .js files (except legacy-reexports and compat) while retaining them for .d.ts files. The legacy-reexport does not have any comments and will be removed with compat in next major version.

npx get-folder-size --folder=dist/package
// 5.88 Mb (with comments)
// 4.63 Mb (without comments)

Roughly 1.25 Mb is saved by removing comments.

Related issue (if exists): #3753

[csvn]

If you are wondering why build_types is slightly out of order in build_all, it's because it has to come before build_legacy_reexports, since the latter uses ./dist/typings.

[coveralls]

Coverage decreased (-0.2%) to 96.656% when pulling ac2976e on csvn:reduce-disk-size into d7bfc9d on ReactiveX:master.

[benlesh]

LGTM... @cartant second opinion?

[cartant]

LGTM

[benlesh]

Thanks @csvn!