Sort inherited products correctly

We pass the filename without the extension to
rblf.inherit(). Removing the extension changes the
sort order when one file's name is a prefix of another:

```
>>> sorted(["base", "base-secondary"])
['base', 'base-secondary']
>>> sorted(["base.mk", "base-secondary.mk"])
['base-secondary.mk', 'base.mk']
```

Correct the sort order so that global variables get
their correct ordering.

Bug: 229132189
Test: ./out/rbcrun ./build/make/tests/run.rbc
Change-Id: I22367eb49b33956b71ac1b966fe78c1308b94257
diff --git a/tests/run.rbc b/tests/run.rbc
index 56ba394..77b6e89 100644
--- a/tests/run.rbc
+++ b/tests/run.rbc
@@ -27,6 +27,7 @@
 load(":board_input_vars.rbc", board_input_vars_init = "init")
 load("//build/make/tests/single_value_inheritance:test.rbc", test_single_value_inheritance = "test")
 load("//build/make/tests/artifact_path_requirements:test.rbc", test_artifact_path_requirements = "test")
+load("//build/make/tests/prefixed_sort_order:test.rbc", test_prefixed_sort_order = "test")
 
 def assert_eq(expected, actual):
     if expected != actual:
@@ -142,3 +143,4 @@
 
 test_single_value_inheritance()
 test_artifact_path_requirements()
+test_prefixed_sort_order()