fix: remove gap if its last element in line (fix flex gap extra spaci…

…ng when children determine parents main axis size) (#1188)

Summary:
Fixes - #35553

## Approach
We're using `betweenMainDim` to add [gap between](https://github.com/intergalacticspacehighway/yoga/blob/bbeede82d36cd89657faf385aaa704f45443c326/yoga/Yoga.cpp#L2495) items in main axis. This is resulting in increased [main axis](https://github.com/intergalacticspacehighway/yoga/blob/bbeede82d36cd89657faf385aaa704f45443c326/yoga/Yoga.cpp#L2598) dimension of the container as it gets added even for the last element. One solution is to keep using it and subtract the gap when last element is reached.

## Aside
Mutating this value feels weird, but I think `betweenMainDim` gets initialized for every line so should be fine? I did some manual tests to verify. I tried running tests but I'll have to downgrade the java version. Let me know if anything fails. Thanks! 🙏

X-link: facebook/yoga#1188

Reviewed By: necolas

Differential Revision: D42078162

Pulled By: NickGerleman

fbshipit-source-id: 0e535618350422e001141a8786a83fc81651afe9

ReactCommon/yoga/yoga/Yoga.cpp

@@ -2540,6 +2540,11 @@ static void YGJustifyMainAxis(
     const YGNodeRef child = node->getChild(i);
     const YGStyle& childStyle = child->getStyle();
     const YGLayout childLayout = child->getLayout();
+    const bool isLastChild = i == collectedFlexItemsValues.endOfLineIndex - 1;
+    // remove the gap if it is the last element of the line
+    if (isLastChild) {
+      betweenMainDim -= gap;
+    }
     if (childStyle.display() == YGDisplayNone) {
       continue;
     }