fix: expand_template propagate runfiles (#1171)

Otherwise the data of the expand_template has to be repeated on
dependents

Fixes https://github.com/r0bobo/rules-py-datafiles-reproducer

Author: alexeagle

lib/private/expand_template.bzl

@@ -60,8 +60,21 @@ def _expand_template_impl(ctx):
         )
 
     all_outs = [output]
-    runfiles = ctx.runfiles(files = all_outs)
-    return [DefaultInfo(files = depset(all_outs), runfiles = runfiles)]
+
+    runfiles = ctx.runfiles(
+        files = all_outs,
+        transitive_files = depset(transitive = [
+            target[DefaultInfo].files
+            for target in ctx.attr.data
+        ]),
+    )
+    return [DefaultInfo(
+        files = depset(all_outs),
+        runfiles = runfiles.merge_all([
+            target[DefaultInfo].default_runfiles
+            for target in ctx.attr.data
+        ]),
+    )]
 
 expand_template_lib = struct(
     doc = """Template expansion