Improve Span API

[stayallive]

Add trace() helper directly on SpanContext:

// Old:
\Sentry\trace(function (\Sentry\State\Scope $scope) use ($processedUsers) {
    // ...
}, \Sentry\Tracing\SpanContext::make()
       ->setOp('function')
       ->setDescription('processing-users')
);

// New:
\Sentry\Tracing\SpanContext::make()
    ->setOp('function')
    ->setDescription('processing-users')
    ->trace(function (\Sentry\State\Scope $scope) use ($processedUsers) {
        // ...
    });

Add data get helper:

// Old:
$span->setData([
    'failure' => $span->getData()['failure'] + 1,
]);

// New:
$span->setData([
    'failure' => $span->getData('failure', 0) + 1,
]);

[cleptric]

Could we split this into two PRs mabye?

[stayallive]

Yes, split into #1766 & #1767