Add dex_import module type

Add a module type for importing a prebuilt jar that contains
classes.dex files.

Test: m with a prebuilt jar that contains classes.dex files in
      PRODUCT_BOOT_JARS
Test: java_test.go, dexpreopt_test.go, dexpreopt_bootjars_test.go
Bug: 124804356
Bug: 125517186

Change-Id: I496848f9dca11f758d49b1cb68168cec7f8e1718

java/dexpreopt_test.go

@@ -119,6 +119,15 @@ func TestDexpreoptEnabled(t *testing.T) {
 				}`,
 			enabled: false,
 		},
+		{
+			name: "dex_import",
+			bp: `
+				dex_import {
+					name: "foo",
+					jars: ["a.jar"],
+				}`,
+			enabled: true,
+		},
 	}
 
 	for _, test := range tests {