Facebook tracking pixel image is converted to `amp-img` instead of `amp-pixel`

[westonruter]

Bug Description

On an AMP-first site I ran across the following amp-img:

<!--noscript-->
<amp-img height="1" width="1" alt="fbpx" src="https://www.facebook.com/tr?id=413752866132374&amp;ev=PageView&amp;noscript=1" class="amp-wp-enforced-sizes amp-wp-6a19fc1 i-amphtml-layout-intrinsic i-amphtml-layout-size-defined" layout="intrinsic" data-amp-original-style="display:inline-block" i-amphtml-layout="intrinsic">
	<i-amphtml-sizer class="i-amphtml-sizer">
		<img alt="" aria-hidden="true" class="i-amphtml-intrinsic-sizer" role="presentation" src="data:image/svg+xml;base64,PHN2ZyBoZWlnaHQ9JzEnIHdpZHRoPScxJyB4bWxucz0naHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmcnIHZlcnNpb249JzEuMScvPg==">
	</i-amphtml-sizer>
	<noscript>
		<img height="1" width="1" alt="fbpx" src="https://www.facebook.com/tr?id=413752866132374&amp;ev=PageView&amp;noscript=1" data-amp-original-style="display:none" class="amp-wp-cb45893">
	</noscript>
</amp-img>
<!--/noscript-->

The Facebook tracking pixel is getting served as an amp-img instead of the more-appropriate amp-pixel. I believe the underlying PHP code where this is coming from is from the Facebook for WooCommerce plugin:

<!-- Facebook Pixel Code -->
<noscript>
<img
	height="1"
	width="1"
	style="display:none"
	alt="fbpx"
	src="https://www.facebook.com/tr?id=<?php echo esc_attr( $pixel_id ); ?>&ev=PageView&noscript=1"
/>
</noscript>
<!-- End Facebook Pixel Code -->

Expected Behaviour

The AMP_Img_Sanitizer should convert images with the https://www.facebook.com/tr URL to amp-pixel instead of amp-img.

There are other tracking pixels out there in the wild which could be accounted for as well.

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Acceptance criteria

Implementation brief

QA testing instructions

Demo

Changelog entry

[westonruter]

QA Passed

I added a Custom HTML block that contained the following:

<!-- Facebook Pixel Code -->
<noscript>
<img
	height="1"
	width="1"
	style="display:none"
	alt="fbpx"
	src="https://www.facebook.com/tr?id=abc123&ev=PageView&noscript=1"
/>
</noscript>
<!-- End Facebook Pixel Code -->

On an AMP page, it came out as expected:

<amp-pixel src="https://www.facebook.com/tr?id=abc123&amp;ev=PageView&amp;noscript=1" layout="nodisplay" class="i-amphtml-layout-nodisplay" hidden="hidden" i-amphtml-layout="nodisplay"></amp-pixel>