Add "allowHTML" option for Markdoc with HTML parsing/processing (#7597)

* 7576 - initial support for HTML inside Markdoc.

This uses htmlparser2 to perform a pure token transform/mutation
on the markdown-it tokens, replacing the original raw HTML string
tokens with a richer set of tokens per HTML node, and in the process
Markdoc tags are interleaved in the resulting token graph at the
appropriate locations

This removes the legacy config of the @astrojs/markdoc integration
entirely (suggested by @bholmesdev) and introduces a new type for
options to be specified in the astro config, initially, with just the new
"enableHTML" option

When "enableHTML" is *not* enabled (the default), the behavior
of the entire @astrojs/markdoc integration should remain functionally
equivalent to before this change

* 7576 - fixed issues with whitespace preservation

also:

* cleaned up " to ' for astro project preferred linting
* made the html rendering test fixture use a dynamic path

* 7576 - detailed nested HTML test coverage

* 7576 -  component + HTML interleaved tests

* 7576 -  fix lint problems from previous changes

* 7576 -  some commentary

* 7576 -  file naming, refactor html under imports, package.json exports definition for html

* 7576

* move out of extensions dir, remove export
* cdata handling changes

* 7576

* inline license from third party code
* cleanup test class copy of HTML output
* remove // third party indicators for imports (clarification: not third party code, just a indicator this group of imports is third party)

* 7576 - fixed test before/after for DRY'ness

* 7576 - no need to React-ify HTML attribute case

* 7576 - rename "enableHTML" option to "allowHTML"

* Added Markdoc allowHTML feature changeset

* 7576 - updated README with allowHTML info

* 7576 - fixed changeset typo

* 7576 - minor edits based on PR feedback for docs

* 7576 - minor edits based on PR feedback for docs

1 files changed, 9 insertions, 0 deletions

diff --git a/packages/integrations/markdoc/test/fixtures/render-html/package.json b/packages/integrations/markdoc/test/fixtures/render-html/package.json
new file mode 100644
index 000000000..4a0c67bfe
--- /dev/null
+++ b/packages/integrations/markdoc/test/fixtures/render-html/package.json
@@ -0,0 +1,9 @@
+{
+  "name": "@test/markdoc-render-html",
+  "version": "0.0.0",
+  "private": true,
+  "dependencies": {
+    "@astrojs/markdoc": "workspace:*",
+    "astro": "workspace:*"
+  }
+}