Fix default values of snapToEnd and snapToStart in ScrollViewProps

Summary:
Changelog: [internal]

Default value for `snapToEnd` and `snapToStart` was incorrect in Fabric. This makes no practical difference as default value is never used (JavaScript always sets true or false).

Default value of `snapToEnd` is true.
https://reactnative.dev/docs/scrollview#snaptoend

Default value of `snapToStart` is true.
https://reactnative.dev/docs/scrollview#snaptostart

Reviewed By: PeteTheHeat

Differential Revision: D27505377

fbshipit-source-id: 73e88aa6ad13a851b8c401e9716fc9a650ec0098

ReactCommon/react/renderer/components/scrollview/ScrollViewProps.cpp

@@ -156,10 +156,13 @@ ScrollViewProps::ScrollViewProps(
           "snapToOffsets",
           sourceProps.snapToOffsets,
           {})),
-      snapToStart(
-          convertRawProp(rawProps, "snapToStart", sourceProps.snapToStart, {})),
+      snapToStart(convertRawProp(
+          rawProps,
+          "snapToStart",
+          sourceProps.snapToStart,
+          true)),
       snapToEnd(
-          convertRawProp(rawProps, "snapToEnd", sourceProps.snapToEnd, {})),
+          convertRawProp(rawProps, "snapToEnd", sourceProps.snapToEnd, true)),
       contentInsetAdjustmentBehavior(convertRawProp(
           rawProps,
           "contentInsetAdjustmentBehavior",