Revert "[Mojo Lite] Remove externs generators and use for-compile generators everywhere."

This reverts commit cd38dfe2c403572af40a6604c82efe4f6a8ad7f2.

Reason for revert: speculative revert for https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/android-cronet-arm-rel/14109

Original change's description:
> [Mojo Lite] Remove externs generators and use for-compile generators everywhere.
> 
> This CL removes the Mojo Lite externs generators and compiles all WebUIs
> with the for-compile targets instead.
> 
> Structurally, all Mojo types are now Closure record typedefs, and their
> generated business logic is underneath a Spec object to prevent the name
> collisions that were happening in the original implementation.
> 
> All goog.requires have also been dropped, and goog.provides are now
> per interface/struct/enum.
> 
> This CL paves the way for generating single file Closure compiled blobs
> that have all the Mojo bindings for a single WebUI.
> 
> TBR=kinuko@chromium.org
> 
> Bug: 914149
> Change-Id: I8866fa9eaa707b2db42369e695ed0a51c373c6b6
> Reviewed-on: https://chromium-review.googlesource.com/c/1476886
> Commit-Queue: calamity <calamity@chromium.org>
> Reviewed-by: Ken Rockot <rockot@google.com>
> Cr-Commit-Position: refs/heads/master@{#634527}

TBR=kinuko@chromium.org,calamity@chromium.org,rockot@google.com

Change-Id: I58267fe8c16088a33fcc067a61b2d869b855a899
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 914149
Reviewed-on: https://chromium-review.googlesource.com/c/1482430
Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
Cr-Commit-Position: refs/heads/master@{#634541}
32 files changed