apex: pass --align-file-size to signapk

APEX files are sized as 4K-aligned so that they can be passed to Guest
OS via block apexes.

Bug: 192991318
Test: check size of built APEX files
Change-Id: I32d988f3cdf2717dbebd87b2ced01840e07a3a9b

apex/builder.go

@@ -761,7 +761,7 @@ func (a *apexBundle) buildUnflattenedApex(ctx android.ModuleContext) {
 	rule := java.Signapk
 	args := map[string]string{
 		"certificates": pem.String() + " " + key.String(),
-		"flags":        "-a 4096", //alignment
+		"flags":        "-a 4096 --align-file-size", //alignment
 	}
 	implicits := android.Paths{pem, key}
 	if ctx.Config().UseRBE() && ctx.Config().IsEnvTrue("RBE_SIGNAPK") {