Add more typescript option validation

[chrisbreiding]

• Closes Add validation for typescript option #46
• Closes Improve error message when attempting to compile TypeScript file and typescript support is not enabled #47

Adds more validation for the typescript option.

If you pass the a non-string for the typescript option, you'll get the following error:

Error running @cypress/browserify-preprocessor:

The 'typescript' option must be a string. You passed: {}

If you pass the a path for the typescript option but nothing exists at that path, you'll get the following error:

Error running @cypress/browserify-preprocessor:

The 'typescript' option must be a valid path to your TypeScript installation. We could not find anything at the following path: /does/not/exist/typescript.js

If you try to preprocess a .ts or .tsx file, but don't have the typescript option set, you'll get the following error:

Error running @cypress/browserify-preprocessor:

You are attempting to preprocess a TypeScript file, but do not have TypeScript configured. Pass the 'typescript' option to enable TypeScript support.

The file: /path/to/cypress/integration/foo_spec.ts`

For the last one, I'm planning to add special handling in Cypress itself. Since we try to set the typescript option for the user, it's opaque when we can't find it but still carry on and try to run TypeScript specs. The user didn't set up the preprocessor themselves, so they can't exactly fix the issue themselves. Instead, when Cypress is handling the preprocessor and encounters this error, it will have a more tailored error message.

[bahmutov]

Good, better errors are super nice

[chrisbreiding]

🎉 This PR is included in version 3.0.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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