Editor: Keep the canvas height stable while resizing the canvas

[t-hamano]

What?

Backport of #81163 to the wp/7.1 branch.

Why?

#81163 does not cherry-pick cleanly onto wp/7.1. The conflicts come entirely from #81248, which removed the dependency group comments across the whole repository on trunk. Those comments are still present on wp/7.1.

How?

Resolved the conflicts in the import blocks only. There are no logic changes relative to the original PR.

Testing Instructions

Same as #81163.

Use of AI Tools

Claude Code was used to identify the cause of the cherry-pick conflicts and to resolve them. The result was reviewed by the author.

[github-actions]

Size Change: +105 B (0%)

Total Size: 7.75 MB

📦 View Changed

Filename	Size	Change
build/scripts/editor/index.min.js	502 kB	+127 B (+0.03%)
build/styles/editor/style-rtl.css	31.2 kB	-4 B (-0.01%)
build/styles/editor/style-rtl.min.css	26.5 kB	-7 B (-0.03%)
build/styles/editor/style.css	31.3 kB	-5 B (-0.02%)
build/styles/editor/style.min.css	26.5 kB	-6 B (-0.02%)

_{compressed-size-action}

[github-actions]

Flaky tests detected in 4948b84.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/31370520971
📝 Reported tests:

should paste block styles using keyboard in /test/e2e/specs/editor/various/list-view.spec.js, passed after 1 failed attempt.

Error: expect(received).toMatchObject(expected)

- Expected  - 6
+ Received  + 0

@@ -1,15 +1,9 @@
  Array [
    Object {
      "attributes": Object {
        "content": "First Block",
-       "style": Object {
-         "color": Object {
-           "background": "#00ff00",
-           "text": "#ff0000",
-         },
-       },
      },
      "name": "core/paragraph",
    },
    Object {
      "attributes": Object {

Call Log:
- Timeout 5000ms exceeded while waiting on the predicate
    at /home/runner/work/gutenberg/gutenberg/test/e2e/specs/editor/various/list-view.spec.js:653:41

[github-actions]

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Co-authored-by: t-hamano <wildworks@git.wordpress.org>

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