This change creates a function in the DataSource interface that
retrieves the nested modules as ModuleInfos given a path to a directory.

Note that proxydatasource is included since it is required to fill the
datasource interface but only returns an empty slice since we are not
implementing the functionality there.

This change also adds a scanModuleInfo helper function for scanning
ModuleInfo from the db.

Updates golang/go#38596

Change-Id: I02f25aad2640a0828e58d622d1c8661e6a303b84
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/253742
Reviewed-by: Julie Qiu <julie@golang.org>

This change adds NestedModules to the directory struct in order to later
render the data in the subdirectories page of a package. We also modify
the createDirectory function to take in a nestedModules parameter.

Updates golang/go#38596

Change-Id: I9bcfc1f2aa37ac0b03b5def4b237473310690af6
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/254018
Reviewed-by: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Julie Qiu <julie@golang.org>

…ectories page

This change adds the HTML and CSS changes for the subdirectories
template to include nested modules in the table with a modules badge.
This includes adding a --light-blue CSS variable to reflect the blue
background of the modules badge.

This change also deletes the _directories.tmpl helper template so that
iterating through the packages and nested modules in the HTML table is a
lot clearer.

before/after images: https://photos.app.goo.gl/2reDtNHxThVnDMiL9

Updates golang/go#38596

Change-Id: Id1dad1ba3a28881a203bf90afe1d5372ede2317c
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/254019
Reviewed-by: Julie Qiu <julie@golang.org>
Reviewed-by: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Jamal Carvalho <jamal@golang.org>