Support identation for XML contributed languages

[angelozerr]

Support identation for XML contributed languages

[datho7561]

There is a bug with linked editing that makes proper tag indentation very annoying. For instance, if you have an .svg document:

<?xml version="1.0" encoding="UTF-8"?>
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://www.w3.org/2000/svg https://www.w3.org/TR/2002/WD-SVG11-20020108/SVG.xsd">
  |
</svg>

If you add a tag <aaa> at the |, hit enter, then type in </aaa>, it will remove content from the opening tag when you type the last >.

This behaviour doesn't happen when you have tag auto closing, since the indentation isn't triggered if you have auto tag closing (eg. in xml and xsd files), but .svg files don't have auto indentation configured by default. However, if you disable auto tag closing, you can see the behaviour in XML and XSD files as well.

[datho7561]

[angelozerr]

@datho7561 I created a PR to try to fix issue with linked editing range at eclipse/lemminx#1457

But the bug that you found is not related to this vscode-xml PR indentation.

[datho7561]

Looks good. Thanks, Angelo!