Fix site editor toolbar when block is bigger than viewport (#43548)

* Take block height and viewport height into account when positioning toolbar

* Move resize prop out of the hook

packages/block-editor/src/components/block-tools/selected-block-popover.js

@@ -132,6 +132,7 @@ function SelectedBlockPopover( {
 			} ) }
 			__unstablePopoverSlot={ __unstablePopoverSlot }
 			__unstableContentRef={ __unstableContentRef }
+			resize={ false }
 			{ ...popoverProps }
 		>
 			{ shouldShowContextualToolbar && (

packages/block-editor/src/components/block-tools/use-block-toolbar-popover-props.js

@@ -15,17 +15,16 @@ import { __unstableUseBlockElement as useBlockElement } from '../block-list/use-
 // down the toolbar will stay on screen by adopting a sticky position at the
 // top of the viewport.
 const DEFAULT_PROPS = {
-	resize: false,
 	flip: false,
 	__unstableShift: true,
 };
 
 // When there isn't enough height between the top of the block and the editor
 // canvas, the `shift` prop is set to `false`, as it will cause the block to be
 // obscured. The `flip` behavior is enabled, which positions the toolbar below
-// the block.
+// the block. This only happens if the block is smaller than the viewport, as
+// otherwise the toolbar will be off-screen.
 const RESTRICTED_HEIGHT_PROPS = {
-	resize: false,
 	flip: true,
 	__unstableShift: false,
 };
@@ -47,7 +46,16 @@ function getProps( contentElement, selectedBlockElement, toolbarHeight ) {
 	const blockRect = selectedBlockElement.getBoundingClientRect();
 	const contentRect = contentElement.getBoundingClientRect();
 
-	if ( blockRect.top - contentRect.top > toolbarHeight ) {
+	// The document element's clientHeight represents the viewport height.
+	const viewportHeight =
+		contentElement.ownerDocument.documentElement.clientHeight;
+
+	const hasSpaceForToolbarAbove =
+		blockRect.top - contentRect.top > toolbarHeight;
+	const isBlockTallerThanViewport =
+		blockRect.height > viewportHeight - toolbarHeight;
+
+	if ( hasSpaceForToolbarAbove || isBlockTallerThanViewport ) {
 		return DEFAULT_PROPS;
 	}