Improve the data-is-breaking check

Context: https://github.com/mono/mono/blob/449e36638fc0b7188b2e9fbd9734a5b263ba9d22/mcs/tools/mono-api-html/HtmlFormatter.cs
Context: https://jenkins.mono-project.com/view/Xamarin.Android/job/xamarin-android-pr-builder-release/143/
Context: mono/mono@c32af89

Every `xamarin-android` PR since [the mono/2018-08 bump][0] has been
**UNSTABLE** because of [API Compatibility Check failures][1].

The "funny" thing is that *there are no API breakages reported*: The
assembly being reported as breaking API -- `Mono.Android.Export.dll`
-- contains *no* public API (!), and thus cannot possibly break it.
Consequently, the [reported API breakage][2] doesn't show anything.

This was quite confusing.

The "cause" of the API breakage reports was the bump to mono/2018-08,
which causes xamarin-android to use a new(er) `mono-api-html` for
`mono-api-info` XML comparison purposes.  The subsequent "cause" is
that the "template HTML" which `mono-api-html` produces is now always
generated when processing `Mono.Android.Export.xml`, seemingly because
`Mono.Android.Export.xml` contains no types at all:

	$ mono ../../bin/BuildDebug/mono-api-html.exe --ignore-changes-parameter-names --ignore-nonbreaking reference/Mono.Android.xml temp/Mono.Android.xml
	# no output

	$ mono ../../bin/BuildDebug/mono-api-html.exe --ignore-changes-parameter-names --ignore-nonbreaking reference/Mono.Android.Export.xml temp/Mono.Android.Export.xml
	# LOTS of output, including lines like
			var any_breaking = element.hasAttribute ('data-is-breaking');

This change was introduced by commit mono/mono@c32af890.

How do we fix this?  A manual review of all locations that
`data-is-breaking` can be generated within `HtmlFormatter.cs` shows
that it will *always* be emitted as the last attribute within an
element, for example:

	<span class='removed removed-method breaking' data-is-breaking>public static void GlClearBufferfi (int, int, float, int);</span>

The simplest fix is to alter the **grep**(1) invocation to check for
`\<data-is-breaking>`, *requiring* the final `>` be matched.

That's the good news.

The bad news is that I've lost faith in using `mono-api-html.exe` as a
mechanism for ensuring that we don't break API.  Events such as this
show that it's *incredibly* brittle -- see also 2c689ef -- and,
worse, *it **still** doesn't work properly*.

Case in point: what happens if we *don't* ignore changes in parameter
names and ignore non-breaking changes in `Mono.Android.xml`?  What
else appears in the output?

	<h3>Type Changed: Android.Media.MediaScannerConnection.IMediaScannerConnectionClient</h3>
	<div>
	<p>Added interface:</p>
	<pre>
	  <span class='added added-interface breaking' data-is-breaking>MediaScannerConnection.IOnScanCompletedListener</span>
	</pre>
	</div>

***WHAT?!***

The ***entire reason*** to use `mono-api-html.exe` -- to at least
*know* when we break API -- does not catch the above breakage.
Altering an interface to implement a new interface is at least a
*possible* breaking change, and does *not* involve parameter names,
yet *it wasn't shown*.

I am not happy to discover this.

This won't be fixed *now*, but a possible idea for future
implementation is to instead use [`Microsoft.DotNet.GenAPI.exe`][3]
from the [mono/api-snapshot][4] module, which is a tool to produce
C# source code for "reference assemblies", which can be compared using
**diff**(1) to see if *anything* changed.

[0]: dotnet/android@3897e86
[1]: https://jenkins.mono-project.com/view/Xamarin.Android/job/xamarin-android-pr-builder-release/143/API_20Compatibility_20Checks/
[2]: https://jenkins.mono-project.com/view/Xamarin.Android/job/xamarin-android-pr-builder-release/143/API_20Compatibility_20Checks/Mono.Android.Export.html
[3]: https://github.com/mono/api-snapshot/tree/master/tools/genapi
[4]: https://github.com/mono/api-snapshot/

Author: jonpryor

Makefile

@@ -94,7 +94,7 @@ check: check-inter-api-level
 	$(call BUILD_API_INFO,temp,$(XA_FRAMEWORK_DIR))
 	failed=0 ; \
 	for file in $(CORE_ASSEMBLIES) $(TFV_ASSEMBLIES) ; do \
-		if $(MONO_API_HTML) $(REFERENCE_DIR)/$$file.xml temp/$$file.xml --ignore-changes-parameter-names --ignore-nonbreaking | grep '\<data-is-breaking\>' > /dev/null 2>&1 ; then \
+		if $(MONO_API_HTML) $(REFERENCE_DIR)/$$file.xml temp/$$file.xml --ignore-changes-parameter-names --ignore-nonbreaking | grep '\<data-is-breaking>' > /dev/null 2>&1 ; then \
 			echo "ABI BREAK IN: $$file.dll" ; \
 			$(MONO_API_HTML) $(REFERENCE_DIR)/$$file.xml temp/$$file.xml  --ignore-changes-parameter-names --ignore-nonbreaking \
 				$(if $(HTML_OUTPUT_DIR),$(HTML_OUTPUT_DIR)/$$file.html); \
@@ -136,7 +136,7 @@ check-inter-api-level: -create-inter-api-infos
 		command="$(MONO_API_HTML) \"$$prev\" \"$$cur\" --ignore-changes-parameter-names --ignore-changes-virtual --ignore-changes-property-setters --ignore-nonbreaking $$extra"; \
 		echo $$command; \
 		eval $$command > "$$out" 2>&1; \
-		if grep '\<data-is-breaking\>' $$out > /dev/null 2>&1 ; then \
+		if grep '\<data-is-breaking>' $$out > /dev/null 2>&1 ; then \
 			echo "<h1>### API BREAK BETWEEN $${_frameworks[$$prev_framework]} and $${_frameworks[$$i]}</h1>" ; \
 			cat $$out; \
 			if [ -n "$(HTML_OUTPUT_DIR)" ]; then \