Add linter for strings.xml.

Strings are tedious to get right, so write a lint script that catches
common errors to warn developers before they're uploaded.

Test: builds, boots
Bug: 76097999
Change-Id: I9826ca796c17cd93a100951d56214653de63a379
diff --git a/PREUPLOAD.cfg b/PREUPLOAD.cfg
index 2a67b75..6c3951d 100644
--- a/PREUPLOAD.cfg
+++ b/PREUPLOAD.cfg
@@ -9,3 +9,5 @@
                       services/usb/
 
 api_lint_hook = ${REPO_ROOT}/frameworks/base/tools/apilint/apilint_sha.sh ${PREUPLOAD_COMMIT}
+
+strings_lint_hook = ${REPO_ROOT}/frameworks/base/tools/stringslint/stringslint_sha.sh ${PREUPLOAD_COMMIT}