Function percentageValue

percentageValue(val: `${number}%` | `-${number}%`): `${number}%` | `-${number}%`
Normalizes a percentage value by parsing and reformatting.

Reference: ST_Percentage in OOXML specification
Parameters
- val: `${number}%` | `-${number}%`
  The percentage string to normalize
Returns `${number}%` | `-${number}%`
The normalized percentage
Example
```
const percent = percentageValue("50.000%"); // Returns "50%"
```
- Defined in util/values.ts:367