Fix: Respect existing val of type='time'

[JGreenlee]

Fixes enketo/enketo#33.

Regression and fix described there, enketo/enketo#33:

I found the change that caused this regression.
3accdd8#diff-caad802f244c59940e6441fa0684b96b8c791470596c23de562f204c2dd1da40

It look like when dropping support for IE, this:

// For IE11, we also need to strip the Left-to-Right marks \u200E...
const ds = `${new Date()
    .toLocaleDateString('en', {
        month: 'short',
        day: 'numeric',
        year: 'numeric',
    })
    .replace(/\u200E/g, '')} ${value.replace(
    /(\d\d:\d\d:\d\d)(\.\d{1,3})(\s?((\+|-)\d\d))(:)?(\d\d)?/,
    '$1 GMT$3$7'
)}`;
const d = new Date(ds);

was simplified to this:

const ds = `${new Date().toLocaleDateString('en', {
    month: 'short',
    day: 'numeric',
    year: 'numeric',
})}`;
const d = new Date(ds);

The intention with that commit was to remove .replace(/\u200E/g, ''), as IE support is no longer needed.
I think that ${value.replace(...) was removed by accident.

---

Here is my proposed fix, which makes it a bit clearer what is actually supposed to happen here.

const todayDate = new Date().toLocaleDateString('en', {
    month: 'short',
    day: 'numeric',
    year: 'numeric',
});
const valueTime = value.replace(
    /(\d\d:\d\d:\d\d)(\.\d{1,3})(\s?((\+|-)\d\d))(:)?(\d\d)?/,
    '$1 GMT$3$7'
);
const d = new Date(`${todayDate} ${valueTime}`);

I will put together a PR for this.

[eyelidlessness]

Thanks!

[lognaturel]

The same raster test is failing as fixed in the last merged PR. So I think we can merge this and it should be green on master, right?