Fix picker value issue

[ethanshar]

Description

Fix how we handle internal picker value change for custom picker in multi mode

Fix #1387

Changelog

Fix issue with Picker with custom renderPicker in multi-select mode not reacting to value change

[M-i-k-e-l]

It seems this is not actually internal, we get here sometimes from external change.
Code for reproduction below (change from external will not work each time):

import _ from 'lodash';
import React, {Component} from 'react';
import {StyleSheet} from 'react-native';
import {View, Text, Card, TextField, Button, Picker, PickerItemValue} from 'react-native-ui-lib'; //eslint-disable-line

export default class PlaygroundScreen extends Component {
  render() {
    return (
      <View bg-dark80 flex padding-20 center>
        <View marginT-20>
          <TextField placeholder="Placeholder" />
        </View>
        <Card height={100} center padding-20>
          <Text text50>Playground Screen</Text>
        </Card>
        <View flex center>
          <Button marginV-20 label="Button"/>
        </View>
        <PickerBug/>
      </View>
    );
  }
}

const styles = StyleSheet.create({
  container: {},
});

class PickerBug extends React.Component {
  state = {
    val: 1
  };

  getNumberPickerRenderer = (label: string | undefined) => (value?: PickerItemValue) => (
    <View padding-20 row>
      <View marginR-s5 flex>
        <Text body>{label}</Text>
      </View>
      <View>
        <Text useCustomTheme bodyBold>
          {value ?? null}
        </Text>
      </View>
    </View>
  );

  numberOptions = [
    {label: '1', value: 1},
    {label: '2', value: 2},
    {label: '3', value: 3}
  ];

  render() {
    return (
      <>
        <Text>Real value: {this.state.val}</Text>
        <Button link onPress={() => this.setState({val: this.state.val + 1})} label="+"/>
        <Button link onPress={() => this.setState({val: this.state.val - 1})} label="-"/>
        <Picker
          migrate
          value={this.state.val}
          onChange={(val: number) => this.setState({val})}
          renderPicker={this.getNumberPickerRenderer('label')}
        >
          {this.numberOptions.map(item => (
            <Picker.Item key={item.value} value={item.value} label={item.label}/>
          ))}
        </Picker>
      </>
    );
  }
}

[ethanshar]

Should be fixed now.