Improve xml.format.splitAttributes settings

Hi.

Currently when xml.format.splitAttributes is set to true, all the attributes appear each on a new line, like this:

<tag
        type="sample"
        name="foo"
        value="bar">

It would be really nice to be able to leave the very first attribute on the same line as the opening tag
and all the other attributes could be aligned by the beginning of this first attribute, like this:

<tag type="sample"
     name="foo"
     value="bar">

Like add an additional option to either leave the first attribute on the same line as the opening tag OR make each attribute appear on a separate line. And if the "leave the first attribute on the same line" is selected then its beginning should be the start of alignment for all the subsequent attributes.

I am just used to how the "XML Tools Plugin" in Notepad++ does it, so I didn't expect to see the first attribute also on a separate line.

Start by tracing the implementation and tests for the xml.format.splitAttributes setting; no specific files are named in the issue. Compare the existing output with the requested option, where the first attribute stays on the opening-tag line and later attributes align with it, and verify both formatting modes.