Rust cdylib/statliclib support for vendor snapshot.

Adds support for platform vendor_available Rust FFI libraries and
binaries to be included in the vendor snapshot.

Because rlib and dylibs are not yet in snapshots, libstd cannot be
included in a vendor snapshot. As a result, vendor-specific Rust code
can't be guaranteed to work with the platform-provided vendor_available
modules built with a newer toolchain. For now, a check is added
indicating vendor-specific Rust code is unsupported.

This changes the linkage for vendor variants of these modules to default
to rlib linkage since dylibs cannot be included in the snapshot yet.

Bug: 184042776
Test: m nothing # new Soong tests pass
Change-Id: I502eaa4bb962eb87ff868fcf49b435f0d2f982e6

rust/image.go

@@ -202,6 +202,8 @@ func (mod *Module) SetImageVariation(ctx android.BaseModuleContext, variant stri
 
 func (mod *Module) ImageMutatorBegin(mctx android.BaseModuleContext) {
 	// Rust does not support installing to the product image yet.
+	vendorSpecific := mctx.SocSpecific() || mctx.DeviceSpecific()
+
 	if Bool(mod.VendorProperties.Product_available) {
 		mctx.PropertyErrorf("product_available",
 			"Rust modules do not yet support being available to the product image")
@@ -217,6 +219,9 @@ func (mod *Module) ImageMutatorBegin(mctx android.BaseModuleContext) {
 			mctx.PropertyErrorf("vendor_ramdisk_available", "cannot be set for rust_ffi or rust_ffi_shared modules.")
 		}
 	}
+	if vendorSpecific {
+		mctx.PropertyErrorf("vendor", "Vendor-only non-rust_ffi Rust modules are not supported.")
+	}
 
 	cc.MutateImage(mctx, mod)