rust: Add common interface for binaries

Structs embedding binaryDecorator (rust_test, rust_benchmark, rust_fuzz)
are binaries as well, but won't pass checks against *binaryDecorator,
such as the check in StaticExecutable().

Add a binaryInterface that can be checked instead to simplify these
checks and ensure we catch all binaries.

Bug: 170672854
Test: rust_test, rust_benchmark return true StaticallyLinked
Change-Id: I2373d3663373a6977260785602a02d39a41320fe

rust/binary.go

@@ -31,6 +31,11 @@ type BinaryCompilerProperties struct {
 	Static_executable *bool `android:"arch_variant"`
 }
 
+type binaryInterface interface {
+	binary() bool
+	staticallyLinked() bool
+}
+
 type binaryDecorator struct {
 	*baseCompiler
 	stripper Stripper
@@ -155,3 +160,11 @@ func (binary *binaryDecorator) stdLinkage(ctx *depsContext) RustLinkage {
 	}
 	return binary.baseCompiler.stdLinkage(ctx)
 }
+
+func (binary *binaryDecorator) binary() bool {
+	return true
+}
+
+func (binary *binaryDecorator) staticallyLinked() bool {
+	return Bool(binary.Properties.Static_executable)
+}