Proposal to add `throwIf` and `throwIfNot` like assert

While working on one of my packages I had a lot of the typical blocks:

```Dart
if (condition)
{
throw (error);
}
```

so I created two functions:

```Dart
void throwIf(bool condition, Object error) {
if (condition) throw (error);
}

void throwIfNot(bool condition, Object error) {
if (!condition) throw (error);
}
```

And have to say it it's super expressive when used in code:

```Dart
throwIf(
instanceName == null,
ArgumentError.value(
T, "Object of type ${T.toString()} is not registered inside GetIt"),
);
throwIfNot(
!(((const Object() is! T) && instanceName != null)),
ArgumentError(
'GetIt: You have to provide either a type OR a name not both.'),
);
```

So I thought wouldn't it be possible to add that to the language?

Cheers and thanks for this awesome SDK

No source file or test is named in the issue. Start by reviewing Dart's existing assert behavior and the language-change process, then define the semantics and specification impact of the proposed throwIf and throwIfNot functions. Done would require an accepted language design with corresponding implementation and validation work identified.

Written by the indexing model from the issue text.