Remove unneeded local variables and comments in Editable and RenderParagraph (#146843)

This PR removes unnecessary local variables and related comments in `Editable` and `RenderParagraph` as both now use another `TextPainter` instance for intrinsics cache.

Test-exempt: minor refactor and comments.

Author: tgucio

packages/flutter/lib/src/rendering/editable.dart

@@ -2312,18 +2312,10 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin,
       ..layout(minWidth: minWidth, maxWidth: maxWidth);
     positionInlineChildren(_textPainter.inlinePlaceholderBoxes!);
     _computeCaretPrototype();
-    // We grab _textPainter.size here because assigning to `size` on the next
-    // line will trigger us to validate our intrinsic sizes, which will change
-    // _textPainter's layout because the intrinsic size calculations are
-    // destructive, which would mean we would get different results if we later
-    // used properties on _textPainter in this method.
-    // Other _textPainter state like didExceedMaxLines will also be affected,
-    // though we currently don't use those here.
-    // See also RenderParagraph which has a similar issue.
-    final Size textPainterSize = _textPainter.size;
+
     final double width = forceLine
       ? constraints.maxWidth
-      : constraints.constrainWidth(_textPainter.size.width + _caretMargin);
+      : constraints.constrainWidth(_textPainter.width + _caretMargin);
     assert(maxLines != 1 || _textPainter.maxLines == 1);
     final double preferredHeight = switch (maxLines) {
       null => math.max(_textPainter.height, preferredLineHeight * (minLines ?? 0)),
@@ -2336,7 +2328,7 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin,
     };
 
     size = Size(width, constraints.constrainHeight(preferredHeight));
-    final Size contentSize = Size(textPainterSize.width + _caretMargin, textPainterSize.height);
+    final Size contentSize = Size(_textPainter.width + _caretMargin, _textPainter.height);
 
     final BoxConstraints painterConstraints = BoxConstraints.tight(contentSize);
 

packages/flutter/lib/src/rendering/paragraph.dart

@@ -809,16 +809,10 @@ class RenderParagraph extends RenderBox with ContainerRenderObjectMixin<RenderBo
     _layoutTextWithConstraints(constraints);
     positionInlineChildren(_textPainter.inlinePlaceholderBoxes!);
 
-    // We grab _textPainter.size and _textPainter.didExceedMaxLines here because
-    // assigning to `size` will trigger us to validate our intrinsic sizes,
-    // which will change _textPainter's layout because the intrinsic size
-    // calculations are destructive. Other _textPainter state will also be
-    // affected. See also RenderEditable which has a similar issue.
     final Size textSize = _textPainter.size;
-    final bool textDidExceedMaxLines = _textPainter.didExceedMaxLines;
     size = constraints.constrain(textSize);
 
-    final bool didOverflowHeight = size.height < textSize.height || textDidExceedMaxLines;
+    final bool didOverflowHeight = size.height < textSize.height || _textPainter.didExceedMaxLines;
     final bool didOverflowWidth = size.width < textSize.width;
     // TODO(abarth): We're only measuring the sizes of the line boxes here. If
     // the glyphs draw outside the line boxes, we might think that there isn't