Export cc vendor functions for usage by rust.

This CL exports and refactors some cc vendor-snapshot related functions
so they can be reused by rust modules to support vendor snapshotting.

Bug: 184042776
Test: m nothing
Change-Id: I12706e62ce0ac3b2b4298085fafc1d77b8e0a0c4
diff --git a/cc/image.go b/cc/image.go
index c6b209f..9370c40 100644
--- a/cc/image.go
+++ b/cc/image.go
@@ -496,7 +496,7 @@
 		// BOARD_VNDK_VERSION. The other modules are regarded as AOSP, or
 		// PLATFORM_VNDK_VERSION.
 		if m.HasVendorVariant() {
-			if isVendorProprietaryModule(mctx) {
+			if IsVendorProprietaryModule(mctx) {
 				vendorVariants = append(vendorVariants, boardVndkVersion)
 			} else {
 				vendorVariants = append(vendorVariants, platformVndkVersion)
@@ -525,7 +525,7 @@
 				platformVndkVersion,
 				boardVndkVersion,
 			)
-		} else if isVendorProprietaryModule(mctx) {
+		} else if IsVendorProprietaryModule(mctx) {
 			vendorVariants = append(vendorVariants, boardVndkVersion)
 		} else {
 			vendorVariants = append(vendorVariants, platformVndkVersion)