Use one mutator for all bp2build conversion.

Each conversion required defining a separate mutator, which will each
operate on _all_ modules and requires each to repeat checks whether the
mutator should operator. Instead, we introduce a single mutator and
modules can define a ConvertWithBp2build to implement bp2build
conversion for that module.

Test: bp2build.sh
Bug: 183079158
Change-Id: I99d4b51f441c2903879092c5b56313d606d4338d
diff --git a/bp2build/bzl_conversion_test.go b/bp2build/bzl_conversion_test.go
index 1e78c0e..f3345a6 100644
--- a/bp2build/bzl_conversion_test.go
+++ b/bp2build/bzl_conversion_test.go
@@ -100,6 +100,7 @@
         # nested_props_ptr start
 #         "nested_prop": attr.string(),
         # nested_props_ptr end
+        "one_to_many_prop": attr.bool(),
         "other_embedded_prop": attr.string(),
         "string_list_prop": attr.string_list(),
         "string_prop": attr.string(),
@@ -128,6 +129,7 @@
         # nested_props_ptr start
 #         "nested_prop": attr.string(),
         # nested_props_ptr end
+        "one_to_many_prop": attr.bool(),
         "other_embedded_prop": attr.string(),
         "string_list_prop": attr.string_list(),
         "string_prop": attr.string(),
@@ -156,6 +158,7 @@
         # nested_props_ptr start
 #         "nested_prop": attr.string(),
         # nested_props_ptr end
+        "one_to_many_prop": attr.bool(),
         "other_embedded_prop": attr.string(),
         "string_list_prop": attr.string_list(),
         "string_prop": attr.string(),