Future#fromCompletionStage(CompletionStage) with Context if it exists

Current version:
```
static Future fromCompletionStage(CompletionStage completionStage) {
Promise promise = Promise.promise();
completionStage.whenComplete((value, err) -> {
```
isn't it better to supply Vert.x context if it "exists"
```
static Future fromCompletionStage(CompletionStage completionStage) {
Context ctx = Vertx.currentContext();
Promise promise = (ctx instanceof ContextInternal) // ⇒ ≠ null
? ((ContextInternal)ctx).promise()
: Promise.promise();
completionStage.whenComplete((value, err) -> {

```