Support multi-cursor auto close tag for elements for different names

[datho7561]

See #490 (comment)

If you have a document like this, with cursors at each | pipe:

<root>
  <aaa|
  <bbb|
  <ccc|
</root>

And then you perform auto-close by typing >, (assuming #490 is merged), it will give:

<root>
  <aaa></aaa>
  <bbb></aaa>
  <ccc></aaa>
</root>

It would be very cool if we instead did:

<root>
  <aaa></aaa>
  <bbb></bbb>
  <ccc></ccc>
</root>

[datho7561]

@JessicaJHee I think this issue won't be too bad. Here are some details about it:

• Here is the relevant VS Code API for accessing the positions of the user's cursor: https://code.visualstudio.com/api/references/vscode-api#TextEditor
• Take a look at tagClosing.ts to see the current implementation. The idea is that we set up a listener that listens to text changes in the current document. When a > or / is inserted, we do a custom request to lemminx to get what should be inserted.
• Here is the code on lemminx that handles the tag closing request: https://github.com/eclipse/lemminx/blob/master/org.eclipse.lemminx/src/main/java/org/eclipse/lemminx/XMLLanguageServer.java#L288
• There are few ways we could implement multi tag closing: either change the API between vscode-xml and lemminx to accept multiple positions, or make multiple requests, one for each cursor position, when we detect that a tag should be closed. There are benefits and drawbacks to each approach.

[angelozerr]

Before working on this issue I think it should be better to work on https://github.com/redhat-developer/vscode-xml because we must align our closingTag request with the autoInsert from html ls