Add HTML Element close tag auto-insertion support

[charlespwd]

The feature's TL;DR:

html-end-auto-insert.mp4

• Type > to close an HTML element, get the </$tagName> for free.

<!-- type this -->
<div id="main">
  <div id="inner">|
</div>

<!-- get this -->
<div id="main">
  <div id="inner">|</div>
</div>

• Type enter in the middle of a closed tag and get the correct level of indentation

enter-ux.mp4

Fun exceptions we support

{% # type %}
<div
  {% if cond > 2 %}
    note="the `>` inside the if condition doesn't trip the parser"
  {% endif %}
>|

{% # get %}
<div
  {% if cond > 2 %}
    note="the `>` inside the if condition doesn't trip the parser"
  {% endif %}
>|</div>

What are you adding in this PR?

• Rearchitect OnTypeFormattingProvider for extensibility
• Add unclosed node information on LiquidHTMLASTParsingErrors
• Add HTML Element close tag auto-insertion support

How it works

• Language Client makes server->client textDocument/onTypeFormatting requests when the user types the > character

  • If the document.ast is a LiquidHTMLASTParsingError that says one of:
    • "Attempting to close X before Y was closed",
    • "Attempting to end parsing before Y was closed",
  • Then we reply with a TextEdit that modifies the file and appends </$tag> at the cursor position
    • When that happens, we also use the window/showDocument server->client request to place the cursor in the right location.

• When the stars are not aligned, we do nothing.

What did you learn?

• The window/showDocument server->client request accepts a selection parameter which makes it possible to move the cursor back to after the > after inserting the </$tagname>.

Before you deploy

• I included a minor bump changeset

[charlespwd]

What I'm doing here is turning this provider into a meta provider like the other ones. I did everything inline for this feature before and I'm rearchitecting to make this like everything else.

[graygilmore]

🎩 went well! Just a couple of nits that can be ignored if you want