test: deflakes blocks e2e (#11640)

The blocks e2e tests were flaky due to how we conditionally render
fields as they enter the viewport. This prevented Playwright from every
reaching the target element when running
`locator.scrollIntoViewIfNeeded()`. This is especially flaky on pages
with many fields because the page size would continually grow as it was
scrolled.

To fix this there are new `scrollEntirePage` and `waitForPageStability`
helpers. Together, these will ensure that all fields are rendered and
fully loaded before we start testing. An early attempt at this was made
via `page.mouse.wheel(0, 1750)`, but this is an arbitrary pixel value
that is error prone and is not future proof.

These tests were also flaky by an attempt to trigger a form state action
before it was ready to receive events. The fix here is to disable any
buttons while the form is initializing and let Playwright wait for an
interactive state.

test/fields/payload-types.ts

@@ -1086,6 +1086,7 @@ export interface CodeField {
   json?: string | null;
   html?: string | null;
   css?: string | null;
+  codeWithPadding?: string | null;
   updatedAt: string;
   createdAt: string;
 }
@@ -2853,6 +2854,7 @@ export interface CodeFieldsSelect<T extends boolean = true> {
   json?: T;
   html?: T;
   css?: T;
+  codeWithPadding?: T;
   updatedAt?: T;
   createdAt?: T;
 }