Improve formatting of Processing Instructions

[anthonyvdotbe]

The formatter formats an XML declaration as follows:

<?xml version="1.0" encoding="UTF-8" ?>

But tools such as Maven generate XML files with an XML declaration as follows (i.e. without a trailing space before the closing tag):

<?xml version="1.0" encoding="UTF-8"?>

This is particularly annoying, because the XML declaration is constantly changed: to version B each time Maven rewrites the XML file (e.g. when doing a release), and then again to version A when the formatter formats the file.

So I think the best option is to format XML declarations as follows:

• if there's already trailing whitespace before the closing tag, collapse it to a single space character
• else, don't add any whitespace

[angelozerr]

I'm fine with this suggestion. @fbricon what do you think?

[fbricon]

how about xml.format.spaceAfterAttribute or xml.format.spaceAfterLastAttribute?

[angelozerr]

After discussion, we should never generate a space before the end of processing instruction. If some user will need that, we will introduce a new settings for that like @fbricon suggested. But for the moment keep simply and don't generate this extra space.

[anthonyvdotbe]

Sounds good to me, thanks.

[angelozerr]

Fixed with eclipse/lemminx#670