dotcom-rendering Refactor `Result` type

A simple version of this type was introduced to see if we would find it useful (#10361). We've started to use it more widely, so this change adds some ergonomic improvements to make it easier to work with. There are three parts to this, as detailed below.

This keeps the convenience functions ok and error for constructing Result, but it's possible these are no longer necessary as the Ok and Err classes could be constructed directly. An update to this may be considered in a future change.

Note: "Hide whitespace" may be useful for reviewing this change.

`kind` Becomes `ok`

The kind property, which was previously of type 'ok' | 'error', has been replaced with an ok property of type boolean. This makes code that checks this property less verbose, and it's similar to the ok property found on the Response type in the Fetch API^1. I believe this was originally suggested by @mxdvl

Before:

if (result.kind === 'ok') {
    console.log(result.value);
} else {
    console.error(result.error);
}

After:

if (result.ok) {
    console.log(result.value);
} else {
    console.error(result.error);
}

New Methods

`map`

Before:

if (result.kind === 'error') {
    return result;
}

return doSomething(result.value);

After:

return result.map(doSomething);

`flatMap`

Before:

if (result.kind === 'error') {
    return result;
}

return doSomethingThatCouldFail(result.value);

After:

return result.flatMap(doSomethingThatCouldFail);

`mapError`

Before:

if (result.kind === 'error') {
    return error(`New error message: ${result.error}`);
}

After:

return result.mapError(err => `New error message: ${err}`);

`okOrThrow` And `errorOrThrow` Become Methods

Previously these were functions, but they have now become methods alongside the others described above. They've also been renamed to better suit the method approach.

Before:

const value = okOrThrow(doSomething(data), 'Expected this to succeed');
const error = errorOrThrow(
    doSomething(data),
    'Expected this to fail',
);

After:

const value = doSomething(data).getOrThrow('Expected this to succeed');
const error = doSomething(data).getErrorOrThrow(
    'Expected this to fail',
);