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, 70 insertions, 0 deletions

diff --git a/packages/integrations/markdoc/src/html/css/style-to-object.ts b/packages/integrations/markdoc/src/html/css/style-to-object.ts
new file mode 100644
index 000000000..7febe3152
--- /dev/null
+++ b/packages/integrations/markdoc/src/html/css/style-to-object.ts
@@ -0,0 +1,70 @@
+// @ts-nocheck
+// https://github.com/remarkablemark/style-to-object
+
+/**
+ * @license MIT
+ * 
+ * The MIT License (MIT)
+ * 
+ * Copyright (c) 2017 Menglin "Mark" Xu <mark@remarkablemark.org>
+ * 
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ * 
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+import { parseInlineStyles } from "./parse-inline-styles.js";
+
+/**
+ * Parses inline style to object.
+ *
+ * @example
+ * // returns { 'line-height': '42' }
+ * styleToObject('line-height: 42;');
+ *
+ * @param  {String}      style      - The inline style.
+ * @param  {Function}    [iterator] - The iterator function.
+ * @return {null|Object}
+ */
+export function styleToObject(style, iterator) {
+  let output = null;
+  if (!style || typeof style !== 'string') {
+    return output;
+  }
+
+  let declaration;
+  let declarations = parseInlineStyles(style);
+  let hasIterator = typeof iterator === 'function';
+  let property;
+  let value;
+
+  for (let i = 0, len = declarations.length; i < len; i++) {
+    declaration = declarations[i];
+    property = declaration.property;
+    value = declaration.value;
+
+    if (hasIterator) {
+      iterator(property, value, declaration);
+    } else if (value) {
+      output || (output = {});
+      output[property] = value;
+    }
+  }
+
+  return output;
+}