mathjs/number missing typescript definitions.

There is still no "mathjs/number" typescript definition.

```typescript
import {
create,
all
} from "mathjs/number";
```
results in typescript error

```
Cannot find module 'mathjs/number' or its corresponding type declarations.ts(2307)
```

There was an issue on this before (#1665). It got closed with reference to #1539. #1539 got closed with a comment asking us to open new issues if there is some issue with the current types. So here I am.