Confusing @model() syntax

In LB3, users could specify model settings at two levels: as a root property or inside `options` property.

See https://stackoverflow.com/q/53307168/69868 for an example of LB3 syntax applied in an LB4 project:

```ts
@model({
settings: {strict: false},
name: 'client',
plural: 'clients',
options: {
mongodb: {
collection: 'clients',
},
},
})
export class Client extends Entity {
// ...
}
```

I am proposing to make two changes in LB4 to help users coming from LB3:

1. Recognize `options` the same way as `settings`. In the example above, `mongodb` settings are not picked by LB4 now. With the proposed change in place, LB4 will set `collection` to `clients` as expected. Alternatively, tell the user setting `options` that they are trying to set an unsupported model-definition property. This can be done at compiler level too.

2. Allow settings to be provided as top-level properties, for example:

```ts
@model({
name: 'client',
strict: false,
mongodb: {
collection: 'clients',
},
})
export class Client extends Entity {
// ...
}
```

Start at the @model() decorator and trace how LB4 reads model settings, comparing that behavior with the LB3 examples in the issue. Resolve whether options should be accepted or rejected and whether top-level settings should be supported; done means the chosen behavior is implemented and verified for the Client examples.

Written by the indexing model from the issue text.