Accept canonical app block paths in block tags

[richpoirier]

What are you adding in this PR?

Theme Check reports a LiquidHTMLSyntaxError for canonical inline app block paths. This change accepts shopify://apps/<app>/blocks/<handle>/<uuid> values in block tags while preserving errors for malformed paths and existing invalid block types.

It also removes duplicate block-name validation from LiquidSyntaxError. The parser now owns block-name validation, so successfully parsed BlockMarkup values are not rejected by a second validator.

App blocks render with the settings their app provides, so LiquidSyntaxError now reports arguments and content on app block paths. This applies to plain arguments and to the block.settings.<id> form. block.name stays allowed. The block parameter checks from #1306 do not report anything for app block paths, because no blocks/*.liquid file exists for them.

{% block 'shopify://apps/example_app/blocks/example-block/00000000-0000-4000-8000-000000000000' %}{% endblock %}                  {% # ok %}
{% block 'shopify://apps/example_app/blocks/example-block/00000000-0000-4000-8000-000000000000', heading: 'Hi' %}{% endblock %}   {% # app blocks do not accept arguments %}
{% block 'shopify://apps/example_app/blocks/example-block/00000000-0000-4000-8000-000000000000' %}Hi{% endblock %}                {% # app blocks do not accept content %}
{% block 'shopify://apps/example_app/snippets/example-block/00000000-0000-4000-8000-000000000000' %}{% endblock %}                {% # not a valid block type %}

Rebased onto #1306 and added a changeset.

[charlespwd]

Can you please add a changeset. Rest of PR looks good to me.