Synchronous text, json, arraybuffer, blob functions

[g105b]

Following off of #88 , this thought needs its own issue...

More often than not, I reach for PhpGt/Fetch only because it's my own library, and not because it's the best tool for the job. I hardly ever actually need to make an asynchronous HTTP call, but I still work with Fetch so that I'm eating my own dogfood.

But if I'm always using it for a simple HTTP request, and I always want the HTTP body without anything else, there should be helper functions on the Http class (and possibly exposed globally like with #88).

My idea would allow something like this:

$json = $http->fetchJson("https://api.example.com/getInfo");
echo "Hello, ", $json->getString("name");

Rather than the current approach:

$http->fetch("https://api.example.com/getInfo")
->then(function(Response $response) {
  return $response->json();
})->then(function(JsonObject $json) {
  echo "Hello, ", $json->getString("name");
});

[g105b]

The way this is achieved in JavaScript:

const response = await fetch("/api");
const jsonObject = await response.json();

This would be nice to replicate in PHP:

$response = $http->awaitFetch("/api");
$jsonObject = $response->awaitJson();