Make native_coverage clause work with ClangCoverage

Make uses NATIVE_COVERAGE to enable gcov coverage and CLANG_COVERAGE
to enable clang coverage.  NATIVE_COVERAGE is translated to the Soong
Native_coverage product variable which triggers the native_coverage
clause in Android.bp files.  The clause also needs to be triggered
for CLANG_COVERAGE.

Rename the existing Native_coverage product variable to GcovCoverage,
and regenerate Native_coverage when either GcovCoverage or
ClangCoverage are set.

Also remove NativeLineCoverage, it wasn't doing anything differently
than Native_coverage.

Bug: 159059537
Test: m checkbuild
Change-Id: I215124a9b35a2ad50ad562079d392e3d33da11f4
diff --git a/apex/apex.go b/apex/apex.go
index a4af7aa..840dd49 100644
--- a/apex/apex.go
+++ b/apex/apex.go
@@ -1553,7 +1553,7 @@
 var _ cc.Coverage = (*apexBundle)(nil)
 
 func (a *apexBundle) IsNativeCoverageNeeded(ctx android.BaseModuleContext) bool {
-	return ctx.Device() && (ctx.DeviceConfig().NativeCoverageEnabled() || ctx.DeviceConfig().ClangCoverageEnabled())
+	return ctx.Device() && ctx.DeviceConfig().NativeCoverageEnabled()
 }
 
 func (a *apexBundle) PreventInstall() {