Create a "Toolchain" API surface

This creates a new API surface for the APIs provided by ART to compile
other API domains (e.g. this contains LambdaMetaFactory). The scope of
this API surface is restricted to compile-time. Unlike the other API
surfaces (e.g. public) whose APIs will exist on device in the form of
implementation libraries, these classes are not guaranteed to exist on
device.

This also updates the naming convention map used in Multi-tree API
export

Bug: 261244752
Test: TH
Change-Id: I164714d68618a3c289bac1a695958e36fdbbda5d

android/sdk_version.go

@@ -51,6 +51,7 @@ const (
 	SdkModule
 	SdkSystemServer
 	SdkPrivate
+	SdkToolchain // API surface provided by ART to compile other API domains
 )
 
 // String returns the string representation of this SdkKind
@@ -76,6 +77,8 @@ func (k SdkKind) String() string {
 		return "module-lib"
 	case SdkSystemServer:
 		return "system-server"
+	case SdkToolchain:
+		return "toolchain"
 	default:
 		return "invalid"
 	}

java/droidstubs.go

@@ -879,6 +879,7 @@ var (
 		"module_lib":    android.SdkModule,
 		"module-lib":    android.SdkModule,
 		"test":          android.SdkTest,
+		"toolchain":     android.SdkToolchain,
 	}
 )