implement aggregate transformer

At present the there is only a simplest aggregate transformer in [echarts-simple-transform/aggregate](https://github.com/100pah/echarts-simple-transform/blob/main/src/aggregate.ts). We should better implement a built-in aggregate transformer in echarts.

## About the API
Think of whether the API of [echarts-simple-transform/aggregate](https://github.com/100pah/echarts-simple-transform/blob/main/src/aggregate.ts) appropriate.

## About group by
In [echarts-simple-transform/aggregate](https://github.com/100pah/echarts-simple-transform/blob/main/src/aggregate.ts) only on dimension can be set in group by. Do we need to support multiple dimension group by?

## About Methods

Some `methods` of aggregate already roughly implemented in [echarts-simple-transform/aggregate](https://github.com/100pah/echarts-simple-transform/blob/main/src/aggregate.ts):
+ `sum`
+ `count`
+ `first`
+ `average`
+ `Q1`
+ `Q2`/`median`
+ `Q3`
+ `min`
+ `max`

We need to make sure they are implemented correctly.

Other methods we may implement:
+ `distinct`: The count of distinct dimension values.
+ `variance`: The sample variance of dimension values.
+ `variancep`: The population variance of dimension values.
+ `stdev`: The sample standard deviation of dimension values.
+ `stdevp`: The population standard deviation of dimension values.
+ `stderr`: The standard error of dimension values.
+ `product`: The product of dimension values.
+ `valid`: The count of dimension values that are not `null`, `undefined`, `''`, `NaN`, `'-'`, or determined by user defined validation function.
+ ... anything else useful?

Some references: [vega aggregate](https://vega.github.io/vega/docs/transforms/aggregate/).

## About math calculation precision

We all known that the floating precision issue (like `0.1 + 0.2`). It might bring trouble in some scenarios like:
+ The math result is needed to be displayed in label.
+ The sum should equal to 100%.
+ Multiple by 100, 1000, ...

Some cases:
```js
0.1 + 0.2 === 0.30000000000000004
2.3 - 0.3 === 1.9999999999999998
33643.2 - 15918.3 === 17724.899999999998
146.39 - 62.83 === 83.55999999999999
1.09 - 0.13 === 0.9600000000000001
0.1 * 0.2 === 0.020000000000000004
16.08 * 100 === 1607.9999999999998
146.39 * 100 === 14638.999999999998
9999999999999999 === 10000000000000000
-11.699999999999986 === -11.699999999999987
```

We should also take care the `toFixed bug` like:
```js
1.005.toFixed(2) === '1.00' // rather than '1.01'
0.1.toFixed(20) === '0.10000000000000000555'
```

**Solution:**
+ A. Do not care about it until some users required.
+ B. Try to resolve it:
+ For arithmetic: use [addSafe](https://github.com/apache/echarts/blob/5.1.2/src/util/number.ts#L286) we already have and implement `multipleSafe` in appropriate place.
+ For comparison of two numbers, use:
```js
const EPSILON = (function () { // Solve compatibility issues
return Number.EPSILON ? Number.EPSILON : Math.pow(2, -52);
})();
function compare(a, b){
return Math.abs(a - b) < EPSILON;
}
```

See: [IEEE 754](https://en.wikipedia.org/wiki/IEEE_floating_point), , , , ... (lots of related references)

Some library:
+
+ [mathjs](https://mathjs.org/)
```js
(math.add(math.bignumber(0.1),math.bignumber(0.2)))
```
+ [decimal.js](http://mikemcl.github.io/decimal.js/)
```js
x = new Decimal(0.1)
y = 0.2
console.log(x.plus(y).toString()
```
+ [bignumber.js](https://github.com/MikeMcl/bignumber.js/blob/master/bignumber.js)
+ [big.js](https://github.com/MikeMcl/big.js/)

## About big number

Do not support.

## Test

Could find some test cases in some other math libraries.