Use cp instead of install for ndk_headers

ndk_headers currently use ctx.Install to install headers in
out/soong/ndk/sysroot. The files are subsequently used to compile ndk
variants of cc libraries on host.

Since these headers are not actually installed on device, use android.Cp
to assemble the NDK sysroot. By itself, it should be a no-op, but
androd.Cp is more friendly with restricting the installation rules to
PRODUCT_PACKAGES.

To make it explicit that the sysroot is not a typical installation path,
this CL also modifies the type to OutputPath

Test: m
Bug: 332778109
Change-Id: I1131c3c764443cbaac525c6022cd09c47695d275
diff --git a/cc/ndk_sysroot.go b/cc/ndk_sysroot.go
index 483d23b..e815172 100644
--- a/cc/ndk_sysroot.go
+++ b/cc/ndk_sysroot.go
@@ -69,12 +69,12 @@
 	ctx.RegisterParallelSingletonType("ndk", NdkSingleton)
 }
 
-func getNdkInstallBase(ctx android.PathContext) android.InstallPath {
+func getNdkInstallBase(ctx android.PathContext) android.OutputPath {
 	return android.PathForNdkInstall(ctx)
 }
 
 // Returns the main install directory for the NDK sysroot. Usable with --sysroot.
-func getNdkSysrootBase(ctx android.PathContext) android.InstallPath {
+func getNdkSysrootBase(ctx android.PathContext) android.OutputPath {
 	return getNdkInstallBase(ctx).Join(ctx, "sysroot")
 }