Add `<slot>` default display style testcase

Testing: Add a new testcase for slot element default disply style.
Fixes: Add slot default display style test for #37174

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Signed-off-by: kongbai1996 <[email protected]>
Signed-off-by: Fuguo <[email protected]>
Co-authored-by: Euclid Ye <[email protected]>

* main: (510 commits)
  DevTools: Fix empty `debugger > source` panel (servo#37197)
  dom: implement signal abort on controller and signal (servo#37192)
  build(deps): bump parking_lot from 0.12.3 to 0.12.4 (servo#37199)
  layout: Split overflow calculation after fragment tree construction (servo#37203)
  build(deps): bump parking_lot_core from 0.9.10 to 0.9.11 (servo#37202)
  build(deps): bump lock_api from 0.4.12 to 0.4.13 (servo#37201)
  build(deps): bump cc from 1.2.24 to 1.2.25 (servo#37198)
  Constellation can now optionally report memory usage when the page is loaded. (servo#37151)
  Implement Input `type=text` UA Shadow DOM (servo#37065)
  constellation: Wait for canvas thread to shut down before shutting down system font service (servo#37182)
  Add slot default display style test (servo#37189)
  Send synthetic keydown/keyup at ime_insert_text (servo#37175)
  script: Let canvas serialization to image fail gracefully (servo#37184)
  Implement basics of link preloading (servo#37036)
  compositor: Add an initial RefreshDriver (servo#37169)
  pixels: Add limitation to max image total bytes length (servo#37172)
  Chore: Remove unused variable in `transition-zero-duration-with-delay.html` (servo#37179)
  build(deps): bump ohos-ime from 0.2.0 to 0.3.0 (servo#37180)
  Add a user agent style for the `<slot>` element (servo#37174)
  build(deps): bump hitrace from 0.1.4 to 0.1.5 (servo#37170)
  ...

In Chromium, the slot user agent stylesheet is located in
[html.css](https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/core/html/resources/html.css;l=1654).

Testing: This change fixes
`tests/wpt/meta/shadow-dom/directionality-001.tentative.html.ini`.

Signed-off-by: kongbai1996 <[email protected]>