fix: 'page-title-updated' event forwarding + documentation

[miniak]

Description of Change

Address #18210.

Checklist

• PR description included and stakeholders cc'd
• npm test passes
  (https://github.com/electron/electron/blob/master/docs/development/testing.md)
• relevant documentation is changed or added
• PR title follows semantic commit guidelines
• PR release notes describe the change in a way relevant to app developers, and are capitalized, punctuated, and past tense.

Release Notes

Notes: Added missing 'page-title-updated' event on webContents to documentation. Also fixed forwarding of the explicitSet argument when emitted on BrowserWindow.

[miniak]

cc @pushkin-

[pushkin-]

@miniak Just to clarify, explicitSet is false when navigating to a page that doesn't explicitly set the title via the <title> tag or through Javascript, and it would only ever be false the first time you navigate to a title-less page. All future page-title-updated calls on that page would have explicitSet set to true - is that correct?

[release-clerk]

Release Notes Persisted

Added missing 'page-title-updated' event on webContents to documentation. Also fixed forwarding of the explicitSet argument when emitted on BrowserWindow.

[trop]

I have automatically backported this PR to "5-0-x", please check out #18318

[trop]

I have automatically backported this PR to "6-0-x", please check out #18319

[trop]

I have automatically backported this PR to "4-2-x", please check out #18320