fix: correct JsxEmit value typo from ReactJsx to ReactJSX

[n3tr]

• Correct ts.JsxEmit typo from ReactJsx to ReactJSX per https://github.com/microsoft/TypeScript/blob/261d03b8ed317475b34cd782d21710f2020a6312/src/compiler/commandLineParser.ts#L5-L11

Verify steps

• yarn create-react-app my-app --template typescript
• cd my-app
• yarn add typescript@4.1.0-beta
• yarn start

[n3tr]

There is another issue here -- By default, if parsedValue is undefined we will try to use value instead

create-react-app/packages/react-scripts/scripts/utils/verifyTypeScriptSetup.js

Line 226 in 027b03b

const valueToCheck = parsedValue === undefined ? value : parsedValue;

but seems like immer() make the object frozen which will cause line

create-react-app/packages/react-scripts/scripts/utils/verifyTypeScriptSetup.js

Line 239 in 027b03b

appTsConfig.compilerOptions[option] = value;

to throw an error

/Users/jirat.ki/Code/lab/cra-ts/node_modules/react-scripts/scripts/utils/verifyTypeScriptSetup.js:242
      appTsConfig.compilerOptions[option] = value;
                                          ^

TypeError: Cannot assign to read only property 'jsx' of object '#<Object>'

I debugged and found

console.log('Object.isFrozen(appTsConfig.compilerOptions)', Object.isFrozen(appTsConfig.compilerOptions))
// Object.isFrozen(appTsConfig.compilerOptions) true

[n3tr]

Closed, duplicated #9921 and #9869