Prevent execution of InputFilter for new lines

[mzorz]

Fix

Fixes #808

This PR avoids handling a new line addition within the InputFilter introduced in #801, especially as it was causing a problem in Span handling when such an insertion was properly being made by FullWidthImageElementWatcher in its method insertVisualNewline(), in occasion of making images separated from paragraphs as per the existing implementation of Aztec in the mentioned TextWatcher.

Explanation

Managed to reproduce this one finding a smaller case - it seemed to me that Aztec was trying to insert an image before a paragraph ending tag, and this is where things seemingly went wrong. Got the hint from looking into the logs of session 5CB4AFF902DF000142875D0BC9D164D7_DNE_0_v2 in case 5c94288ef8b88c296305c342-fabric.

Using this following HTML code as per a blog Post body on WPAndroid:

<p style="box-sizing:border-box;">This is just a test.</p>

1. visual mode, tap and place the cursor right BEFORE the DOT, like this: This is just a test|.
2. now, try inserting an image from the device (tap the cross, the media picker shows up, tap on an image, tap the check/done icon on the top-right corner of the screen)
3. observe the crash

First of all, the filter shouldn't be activated by this condition, as this is not what we wanted to capture originally. The situation that we meant to capture was the addition of a character right before an AztecImageSpan, and this is effectively an insertion of a character but it's being done artificially (and on purpose) by Aztec during this operation as can be seen in the stacktrace.

 at org.wordpress.aztec.AztecText$setupKeyListenersAndInputFilters$dynamicLayoutCrashPreventer$1.filter(AztecText.kt:483)
        at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:514)
        at android.text.SpannableStringBuilder.insert(SpannableStringBuilder.java:224)
        at android.text.SpannableStringBuilder.insert(SpannableStringBuilder.java:222)
        at org.wordpress.aztec.watchers.FullWidthImageElementWatcher.insertVisualNewline(FullWidthImageElementWatcher.kt:34)
        at org.wordpress.aztec.watchers.FullWidthImageElementWatcher.normalizeEditingAroundImageSpans(FullWidthImageElementWatcher.kt:67)
        at org.wordpress.aztec.watchers.FullWidthImageElementWatcher.afterTextChanged(FullWidthImageElementWatcher.kt:30)
        at android.widget.TextView.sendAfterTextChanged(TextView.java:9380)
        at android.widget.TextView$ChangeWatcher.afterTextChanged(TextView.java:11939)
        at android.text.SpannableStringBuilder.sendAfterTextChanged(SpannableStringBuilder.java:1262)
        at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:574)
        at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:504)
        at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:502)
        at org.wordpress.aztec.formatting.LineBlockFormatter.insertMedia(LineBlockFormatter.kt:160)
        at org.wordpress.aztec.formatting.LineBlockFormatter.insertImage(LineBlockFormatter.kt:135)
        at org.wordpress.aztec.AztecText.insertImage(AztecText.kt:1730)

See specifically:

        at org.wordpress.aztec.watchers.FullWidthImageElementWatcher.insertVisualNewline(FullWidthImageElementWatcher.kt:34)
        at org.wordpress.aztec.watchers.FullWidthImageElementWatcher.normalizeEditingAroundImageSpans(FullWidthImageElementWatcher.kt:67)

So, this PR lets that particular situation happen as it shouldn't be captured by the InputFilter.

Test

Using WPAndroid on Android 8.0 or 8.1, make sure to use the commit hash aztecVersion = '89f94f0407dffba19227cdfeba8a5981b1570344'

1. visual mode, tap and place the cursor right BEFORE the DOT, like this: This is just a test|.
2. now, try inserting an image from the device (tap the cross, the media picker shows up, tap on an image, tap the check/done icon on the top-right corner of the screen)
3. observe there's not a crash anymore.

Also, verify the case described in #729 doesn't crash.

[daniloercoli]

LGTM!