KCL: No 'let' or 'const' required when declaring vars (#4063)

Previously variable declaration required a keyword, e.g.

```kcl
let x = 4
const x = 4
var x = 4
```

These were all valid, and did the exact same thing. As of this PR, they're all still valid, but the KCL formatter will change them all to just:

```kcl
x = 4
```

which is the new preferred way to declare a constant. 

But the formatter will remove the var/let/const keywords.

Closes https://github.com/KittyCAD/modeling-app/issues/3985

e2e/playwright/testing-settings.spec.ts

@@ -596,14 +596,14 @@ test.describe('Testing settings', () => {
     await page.addInitScript(() => {
       localStorage.setItem(
         'persistCode',
-        `const sketch001 = startSketchOn('XZ')
+        `sketch001 = startSketchOn('XZ')
   |> startProfileAt([0, 0], %)
   |> line([5, 0], %)
   |> line([0, 5], %)
   |> line([-5, 0], %)
   |> lineTo([profileStartX(%), profileStartY(%)], %)
   |> close(%)
-const extrude001 = extrude(5, sketch001)
+extrude001 = extrude(5, sketch001)
 `
       )
     })