Handle extension dependencies in the installer

Handle extension dependencies in the installer

As there will likely be extensions bundled with the 1.31 release that
depend upon other extensions, we should have the installer prevent users
from enabling extensions that depend on other, not-enabled extensions.

We can build a dependency map from extension.json's "requires"
component. On the client-side, we'll first disable all checkboxes that
require other extensions, and evaluate each checkbox click, updating the
disabled checkboxes as possible.

This required some refactoring of how ExtensionRegistry reports issues
with dependency resolution so we could get a list of what was missing.

While we're at it, sort the extensions under headings by type.

This does not support skins that have dependencies yet (T186092).

Bug: T31134
Bug: T55985
Change-Id: I5f0e3b1b540b5ef6f9b8e3fc2bbaad1c65b4b680