Migration of jsx files to tsx 3 (#851)

This is in continue to:
- #850
- #848

The last files should be converted as part of this PR, there are only a
handful left.

src/components/Block.tsx

@@ -12,7 +12,7 @@ type BlockProps = {
   onChange?(...args: unknown[]): unknown
   fieldSpec?: object
   wideMode?: boolean
-  error?: unknown[]
+  error?: {message: string}
 };
 
 type BlockState = {