Add apex compat symlinks to LOCAL_SOONG_INSTALL_SYMLINKS

We want to make FULL_SYSTEMIMAGE_DEPS more accurate so that we can
remove the need for `m installclean`.

Currently, the compat symlinks are installed by adding them as
dependencies of other installed files. Doing this doesn't end up
propagaing the compat symlinks all the way to FULL_SYSTEMIMAGE_DEPS.

Add them to LOCAL_SOONG_INSTALL_SYMLINKS, which will cause them to
be propagated to FULL_SYSTEMIMAGE_DEPS.

Bug: 205632228
Test: Full build with a change to delete files not in FULL_SYSTEMIMAGE_DEPS from the staging dir
Change-Id: Idc7fc0a0dbf7c8ac3f0628c16413cd1df69a7821
diff --git a/apex/prebuilt.go b/apex/prebuilt.go
index 3509e6c..f2e87c8 100644
--- a/apex/prebuilt.go
+++ b/apex/prebuilt.go
@@ -235,6 +235,7 @@
 					entries.SetString("LOCAL_MODULE_STEM", p.installFilename)
 					entries.SetPath("LOCAL_SOONG_INSTALLED_MODULE", p.installedFile)
 					entries.SetString("LOCAL_SOONG_INSTALL_PAIRS", p.outputApex.String()+":"+p.installedFile.String())
+					entries.AddStrings("LOCAL_SOONG_INSTALL_SYMLINKS", p.compatSymlinks.Strings()...)
 					entries.SetBoolIfTrue("LOCAL_UNINSTALLABLE_MODULE", !p.installable())
 					entries.AddStrings("LOCAL_OVERRIDES_MODULES", p.prebuiltCommonProperties.Overrides...)
 					p.addRequiredModules(entries)