fix: 'Types of property 'content' are incompatible.' in Toast and add demo

[erichua23]

First of all, thank you for your contribution! :-)

Please makes sure that these checkboxes are checked before submitting your PR, thank you!

• [x] Make sure that you follow antd's code convention.
• [x] Run npm run lint and fix those errors before submitting in order to keep consistent code style.
• [x] Rebase before creating a PR to keep commit history clear.
• [x] Add some descriptions and refer relative issues for you PR.

Extra checklist:

if isBugFix :

• [x] Make sure that you add at least one unit test for the bug which you had fixed.

elif isNewFeature :

• [ ] Update API docs for the component.
• [ ] Update/Add demo to demonstrate new feature.
• [ ] Update TypeScript definition for the component.
• [ ] Add unit tests for the feature.

fix: 'Types of property 'content' are incompatible.' in Toast and add demo.

caused by this PR. https://github.com/ant-design/ant-design-mobile-rn/pull/1160

Add test case for custom view in Toast.

[1uokun]

awsome🎉