Copy the placeholders and spaces to the translation textarea

[amieiro]

Problem

In #1620 we introduced a wrapper to highlight the placeholders, and in #1500 we introduced a similar wrapper to highlight leading and trailing spaces, and double/multiple spaces in the middle.

When a translator clicks on some of these elements, they are not copied to the translation textarea when you click on the placeholder or in the space.

Solution

This PR adds this improvement, so when you click on one of these gray squares (see the screenshot below), this item (placeholders or space) is copied to the translation textarea, where the cursor is placed.

[fxbenard]

As all those spaces are usually wrong or bad and have no place in the translation, I don't see the point of such a feature.

[amieiro]

@fxbenard I totally agree. These spaces are usually a programming error, but the translations need them, because the developer needs these spaces in the translation, so I think it is an improvement to give this functionality to the translators.

[fxbenard]

@amieiro As said as those are mostly errors in the source code, i don't get why they're important in the translations. BTW most translators remove them.
A better way to notify devs about those will be a better improvement that allowing those errors to be pushed across TMs
My 2 cts…. But thanks for this anyway.