List bullet positioning and first line paragraph spacing before

Summary: If something is the first line in the document, TextKit doesn't apply a paragraphSpacingBefore value. Our list bullet drawing code compensates for paragraphSpacingBefore. This was causing us to draw incorrectly positioned bullets if paragraphSpacingBefore was used and the list was the first thing in the document.

Differential Revision: D54380971

fbshipit-source-id: 04156ede936686c74c1294ab612430570c55c596

Plugins/LexicalListPlugin/LexicalListPlugin/ListPlugin.swift

@@ -52,14 +52,16 @@ open class ListPlugin: Plugin {
           return
         }
 
+        let isFirstLine = (glyphRange.location == 0)
+
         var attributes = textStorage.attributes(at: characterRange.location, effectiveRange: nil)
 
         var spacingBefore = 0.0
         if let paragraphStyle = attributes[.paragraphStyle] as? NSParagraphStyle, let mutableParagraphStyle = paragraphStyle.mutableCopy() as? NSMutableParagraphStyle {
           mutableParagraphStyle.headIndent = 0
           mutableParagraphStyle.firstLineHeadIndent = 0
           mutableParagraphStyle.tailIndent = 0
-          spacingBefore = paragraphStyle.paragraphSpacingBefore
+          spacingBefore = isFirstLine ? 0 : paragraphStyle.paragraphSpacingBefore
           mutableParagraphStyle.paragraphSpacingBefore = 0
           attributes[.paragraphStyle] = mutableParagraphStyle
         }