[orca] Fall back on "placeholder" when "placeholder-text" is not used

[Joanmarie Diggs <joanied src gnome org>]

commit ef231ec602d94245a6c8ccd142952f273eeadbbb
Author: Joanmarie Diggs <jdiggs igalia com>
Date:   Tue Jul 14 18:29:04 2020 +0200

    Fall back on "placeholder" when "placeholder-text" is not used
    
    While "placeholder-text" usage predates aria-placeholder, some user agent
    implementors would prefer to expose placeholder text using "placeholder"
    because doing so is consistent with the convention used for other ARIA
    properties. So check for both.

 src/orca/generator.py | 4 ++++
 1 file changed, 4 insertions(+)
---
diff --git a/src/orca/generator.py b/src/orca/generator.py
index 862b6ae2d..5d3aedc03 100644
--- a/src/orca/generator.py
+++ b/src/orca/generator.py
@@ -369,6 +369,10 @@ class Generator:
         if placeholder:
             return [placeholder]
 
+        placeholder = attrs.get('placeholder')
+        if placeholder:
+            return [placeholder]
+
         return []
 
     def _generateLabelAndName(self, obj, **args):