java_sdk_library - Allow it to be replaced by prebuilt

Previously, a java_sdk_library called "SDKLIB" would create a
prebuilt_etc module called "SDKLIB.xml" which installs the generated
XML permission file to /etc/permissions/SDKLIB.xml. That module
depended on the java_sdk_library "SDKLIB" to generate the XML file
as one of its outputs by specifying srcs: [":SDKLIB{.xml}"].

If the java_sdk_library is replaced by a prebuilt then the SDKLIB.xml
module expects the prebuilt to provide the XML permissions file which
it doesn't because that is an implementation detail and so the build
breaks.

A couple of alternative approaches were looked at to fix this. One was
to have the logic that replaced the source module with the prebuilt to
inform the source module that it was being replaced so it could disable
its created module. That lead to a dependency cycle where
    SDKLIB -> SDKLIB.xml -> SDKLIB{.xml}

Another solution was to mark dependency tags in such a way that the
prebuilt could automatically identify and disable the SDKLIB.xml
module. Similar to how the visibility code will ignore dependencies
that are tagged with ExcludeFromVisibilityEnforcementTag. That became
very convoluted.

Instead the java_sdk_library was changed so that it was not responsible
for creating the XML permissions file. Instead it created a genrule
called "gen-SDKLIB.xml" to create it and then "SDKLIB.xml" depended on
that. The java_sdk_library also depended on the genrule to make the XML
permissions file available for APEX and testing.

Some refactoring of the APEX code and tests was necessary because they
had knowledge of the internal implementation of java_sdk_library. The
refactoring insulates them a little better from those details.

Bug: 148080325
Test: m droid && TARGET_BUILD_APPS=Camera2 m
Change-Id: I597bccbb177b6b6320c3a3edeff467243230d384