Rename script/fetch-policy to script/commit-current-upstream-policy-docs

sneak, on the PR: the script does more than fetch, and short names are
not wanted. The make target, the test names, the variables and the
messages take the new name. Behaviour is unchanged.

Model: opus-5-5

README.md

@@ -141,13 +141,14 @@ alpine. We provide:
   `script/check`
 - `script/install-precommit` — installs the git pre-commit hook (our own
   extension); `make hooks` shims to it
-- `script/fetch-policy` — fetch the vendored policy files from this repo over
-  HTTP and write them into a repo (our own extension). It writes into the repo
-  given as its argument, or its own repo with no argument. It stops when its
-  target is this repo.
-- `script/update-policy` — fetch the current `script/fetch-policy`, run it on
-  its own repo and commit the result without pushing (our own extension). It is
-  for the repos that vendor the policy files. It stops when run here.
+- `script/commit-current-upstream-policy-docs` — fetch the vendored policy files
+  from this repo over HTTP and write them into a repo (our own extension). It
+  writes into the repo given as its argument, or its own repo with no argument.
+  It stops when its target is this repo.
+- `script/update-policy` — fetch the current
+  `script/commit-current-upstream-policy-docs`, run it on its own repo and
+  commit the result without pushing (our own extension). It is for the repos
+  that vendor the policy files. It stops when run here.
 
 `make hooks` installs the pre-commit hook that runs `script/precommit`.