Set min_sdk_version (for non-mainline files)

Modules contributing mainline modules (APK/APEX) should set
min_sdk_version as well as apex_available.

For now setting min_sdk_version doesn't change build outputs.
But build-time checks will be added soon.

This is second part of two CLs: covers non-mainline files

Exempt-From-Owner-Approval: cherry-pick from internal branch

Bug: 152655956
Test: m
Merged-In: I55336e644990d3f175e0c011856b52ec600e452a
Change-Id: I55336e644990d3f175e0c011856b52ec600e452a
(cherry picked from commit e3cf41a2806834c4d678a78534134aeee4e12cc5)
diff --git a/media/libmediahelper/Android.bp b/media/libmediahelper/Android.bp
index ae135af..b46c98a 100644
--- a/media/libmediahelper/Android.bp
+++ b/media/libmediahelper/Android.bp
@@ -1,6 +1,7 @@
 cc_library_headers {
     name: "libmedia_helper_headers",
     vendor_available: true,
+    min_sdk_version: "29",
     export_include_dirs: ["include"],
     host_supported: true,
     target: {