Replace http with https entering a video link

[Presskopp]

Using the classic editor / classic block:

1) Add Media
2) Insert from URL

A field appears prefilled with "​http://"

Just like in #46312 this should be changed to "​https://" (or even not be prefilled at all)

Some quotes from slack(core-media):

@adamsilverstein:

https as the default suggested prefix makes sense to me

@joyously:

even better is to match the placeholder to the scheme of the site

@joedolson:

If there's going to be a default, I think that ​https:// makes the most sense, but I'm not sure there should be a default at all. Perhaps there should be a placeholder that defaults to the site's protocol, but I don't think any content should be prefilled.

Using Gutenberg:

1) Add Video Block
2) Insert from URL

A field appears having no prefilled value

---

Besides of this there's more to consider:

Using the classic editor / classic block:

During typing WP already tries to make a connection to the entered URL. In case the site uses https, if http is used, the browser (chrome used here) throws a warning about mixed content in console and switches automatically to https.
ALSO: If entered a decimal URL a conversion takes place, for example ​http://134744072 will be converted to ​http://8.8.8.8/
Whatever will be entered, the console fills up with warnings BUT there will be no warning or error visible in the backend. I can enter whatever and it will be pasted as Video-URL unchanged.
So we don't need those connection attempts at all here.

Using Gutenberg:

In Gutenberg the URL will only be checked after pressing enter.