Fix bug with undo startSketchOn removing existing sketch (#6834)

* Fix bug with `undo startSketchOn` removing existing sketch

Fixes #6822, I believe. in this case the `variableName` was not being
marked as in-use, so I just logged out the AST and made sure this case
was covered. @Irev-Dev this is probably worth a check from you.

* Add a regression test

It's an E2E test because I'm being lazy, but it should probably be an
XState unit test at some point.

* check what's checked

---------

Co-authored-by: Kurt Hutten <k.hutten@protonmail.ch>

src/components/ModelingMachineProvider.tsx

@@ -751,13 +751,22 @@ export const ModelingMachineProvider = ({
               if (err(varDec)) return reject(new Error('No varDec'))
               const variableName = varDec.node.declaration.id.name
               let isIdentifierUsed = false
-              traverse(newAst, {
-                enter: (node) => {
-                  if (node.type === 'Name' && node.name.name === variableName) {
-                    isIdentifierUsed = true
-                  }
-                },
-              })
+              const isInitAPipe =
+                varDec.node.declaration.init.type === 'PipeExpression'
+              if (isInitAPipe) {
+                isIdentifierUsed = true
+              } else {
+                traverse(newAst, {
+                  enter: (node) => {
+                    if (
+                      node.type === 'Name' &&
+                      node.name.name === variableName
+                    ) {
+                      isIdentifierUsed = true
+                    }
+                  },
+                })
+              }
               if (isIdentifierUsed) return
 
               // remove body item at varDecIndex