feat: add request.body async getters

[hbenl]

Fixes #38150 and the following tests:

with Chrome/CDP:

• page/network-request-body.spec.ts:
  • "should get request body for file/blob"
  • "should get request body for navigator.sendBeacon api calls"

with BiDi:

• page/network-request-body.spec.ts:
  • "should return correct request body buffer for utf-8 body"
  • "should return request body w/o content-type"
  • "should throw on invalid JSON in post data"
  • "should return body for PUT requests"
  • "should get request body for file/blob"
  • "should get request body for navigator.sendBeacon api calls"
• page/page-network-request.spec.ts:
  • "should parse the data if content-type is application/x-www-form-urlencoded" (Firefox only)
  • "should parse the data if content-type is application/x-www-form-urlencoded; charset=UTF-8"
  • "should parse the json post data"
  • "should return multipart/form-data" (Firefox only)
  • "should return postData"
  • "should work with binary post data" (Firefox only)
  • "should work with binary post data and interception" (Firefox only)
• page/page-request-intercept.spec.ts:
  • "request.body is not null when fetching FormData with a Blob" (Firefox only)
  • "should intercept multipart/form-data request body" (Firefox only)
• page/page-route.spec.ts:
  • "should intercept when postData is more than 1MB"

[github-actions]

Test results for "MCP"

1 failed
❌ [webkit] › mcp/test-debug.spec.ts:48 › test_debug (pause/resume) @mcp-macos-15

2821 passed, 116 skipped

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Merge workflow run.

[github-actions]

Test results for "tests 1"

8 failed
❌ [playwright-test] › aria-snapshot-file.spec.ts:225 › should respect config.expect.toMatchAriaSnapshot.pathTemplate @macos-latest-node20
❌ [playwright-test] › playwright.spec.ts:853 › should allow dynamic import in evaluate @macos-latest-node20
❌ [playwright-test] › playwright.spec.ts:877 › page.pause() should disable test timeout @macos-latest-node20
❌ [playwright-test] › playwright.spec.ts:914 › window.playwright should not override existing property @macos-latest-node20
❌ [playwright-test] › aria-snapshot-file.spec.ts:40 › should generate multiple missing @windows-latest-node20
❌ [playwright-test] › aria-snapshot-file.spec.ts:62 › should rebaseline all @windows-latest-node20
❌ [playwright-test] › reporter-html.spec.ts:1037 › created › should have link for opening HTML attachments in new tab @macos-latest-node20
❌ [playwright-test] › update-aria-snapshot.spec.ts:226 › should generate baseline with special characters @macos-latest-node20

6 flaky

⚠️ [chromium-library] › library/page-close.spec.ts:162 › should not treat navigations as new popups `@chromium-ubuntu-22.04-node24`
⚠️ [webkit-page] › page/page-network-request.spec.ts:288 › should parse the data if content-type is application/x-www-form-urlencoded `@webkit-ubuntu-22.04-node20`
⚠️ [playwright-test] › ui-mode-trace.spec.ts:688 › should indicate current test status `@macos-latest-node20`
⚠️ [playwright-test] › ui-mode-trace.spec.ts:796 › should update state on subsequent run `@macos-latest-node20`
⚠️ [playwright-test] › ui-mode-trace.spec.ts:748 › should partition action tree state by test `@ubuntu-latest-node22`
⚠️ [playwright-test] › ui-mode-trace.spec.ts:748 › should partition action tree state by test `@windows-latest-node20`

34438 passed, 696 skipped

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Merge workflow run.

[hbenl]

The failing BiDi tests are all passing locally. CI test results seem flakier than they used to be, perhaps due to the increased number of workers.