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/rust/coverage.go b/rust/coverage.go
index 9be57dc..4e3977b 100644
--- a/rust/coverage.go
+++ b/rust/coverage.go
@@ -45,7 +45,7 @@
 
 func (cov *coverage) flags(ctx ModuleContext, flags Flags, deps PathDeps) (Flags, PathDeps) {
 
-	if !ctx.DeviceConfig().NativeCoverageEnabled() && !ctx.DeviceConfig().ClangCoverageEnabled() {
+	if !ctx.DeviceConfig().NativeCoverageEnabled() {
 		return flags, deps
 	}