Support registerTransform in echarts.use

### What problem does this feature solve?
Expose the ability of registerTransform in a neat way.

### What does the proposed API look like?
```ts
import * as echarts from 'echarts';
import * as ecStat from 'ecStat';

// call registerTransform internally for all transformers in ecStat.
echarts.use(ecStat);
```
And
```ts
import * as echarts from 'echarts';
import {histogram} from 'ecStat/transform';

// call registerTransform internally.
echarts.use(histogram);
```

See ecomfe/echarts-stat#36

Start by tracing the existing echarts.use API and the registerTransform references in the codebase. Compare the behavior with ecomfe/echarts-stat#36; done means both shown usage forms work, including passing the full ecStat module and an individual histogram transformer.

Written by the indexing model from the issue text.