Minimize EditText Spans 1/9: Fix precedence (facebook#36543)

Summary:
Pull Request resolved: facebook#36543

This is part of a series of changes to minimize the number of spans committed to EditText, as a mitigation for platform issues on Samsung devices. See this [GitHub thread]( facebook#35936 (comment)) for greater context on the platform behavior.

We cache the backing EditText span on text change to later measure. To measure outside of a TextInput we need to restore any spans we removed. Spans may overlap, so base attributes should be behind everything else.

The logic here for dealing with precedence is incorrect, and we should instead accomplish this by twiddling with the `SPAN_PRIORITY` bits.

Changelog:
[Android][Fixed] - Minimize Spans 1/N: Fix precedence

Differential Revision: https://internalfb.com/D44240779

fbshipit-source-id: b20e9300b1f7642bef055ca9ed20fd6a53ec3fbe

Author: NickGerleman

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/views/textinput/ReactEditText.java

@@ -683,29 +683,18 @@ private void stripAttributeEquivalentSpans(SpannableStringBuilder sb) {
     }
   }
 
-  private void unstripAttributeEquivalentSpans(
-      SpannableStringBuilder workingText, Spannable originalText) {
-    // We must add spans back for Fabric to be able to measure, at lower precedence than any
-    // existing spans. Remove all spans, add the attributes, then re-add the spans over
-    workingText.append(originalText);
+  private void unstripAttributeEquivalentSpans(SpannableStringBuilder workingText) {
+    int spanFlags = Spannable.SPAN_INCLUSIVE_INCLUSIVE;
 
-    for (Object span : workingText.getSpans(0, workingText.length(), Object.class)) {
-      workingText.removeSpan(span);
-    }
+    // Set all bits for SPAN_PRIORITY so that this span has the highest possible priority
+    // (least precedence). This ensures the span is behind any overlapping spans.
+    spanFlags |= Spannable.SPAN_PRIORITY;
 
     workingText.setSpan(
         new ReactAbsoluteSizeSpan(mTextAttributes.getEffectiveFontSize()),
         0,
         workingText.length(),
-        Spanned.SPAN_INCLUSIVE_INCLUSIVE);
-
-    for (Object span : originalText.getSpans(0, originalText.length(), Object.class)) {
-      workingText.setSpan(
-          span,
-          originalText.getSpanStart(span),
-          originalText.getSpanEnd(span),
-          originalText.getSpanFlags(span));
-    }
+        spanFlags);
   }
 
   private static boolean sameTextForSpan(
@@ -1132,8 +1121,8 @@ private void updateCachedSpannable(boolean resetStyles) {
       // ...
       // - android.app.Activity.dispatchKeyEvent (Activity.java:3447)
       try {
-        Spannable text = (Spannable) currentText.subSequence(0, currentText.length());
-        unstripAttributeEquivalentSpans(sb, text);
+        sb.append(currentText.subSequence(0, currentText.length()));
+        unstripAttributeEquivalentSpans(sb);
       } catch (IndexOutOfBoundsException e) {
         ReactSoftExceptionLogger.logSoftException(TAG, e);
       }