Mark espresso prebuilts as java:sdk

The prebuilts didn't have LOCAL_SDK_VERSION, which in turn made them
categorized as java:platform which can only be referenced from other
java:platform modules. This means that an app built with
LOCAL_SDK_VERSION can't use these prebuilts. This has been working since
java:sdk -> java:platform dependency violation was only a warning, but
this will soon be an error.

In order to avoid the expected link-type check error, correctly mark the
espresso prebuilts as java:sdk by adding LOCAL_SDK_VERSION value.

Bug: 69899800
Test: mma -j under this directory
Change-Id: I783c7a560b4d60a69e759839d4ffdab266e25f9f