feat: add multi BrowserView support to BrowserWindow

[summeroff]

Description of Change

new feature: multi browser views support for BrowserWindow

Add functions addBrowserView, removeBroserView, getBrowserViews to BrowserWindow class.

Existing API setBrowserView and getBrowserView changed to use new API inside.

This functionality was mentioned in the initial BrowserView feature PR #9166 . And asked few times since then. Recently in a discussion #10622 .

It is a resubmit of PR #16064 as changes moved to master branch instead of 2-0-x branch.
/cc @zcbenz

Checklist

• PR description included and stakeholders cc'd
• npm test passes
• tests are added
• relevant documentation is changed or added
• PR title follows semantic commit guidelines

Release Notes

Notes: Added support for multiple browser views per BrowserWindow.

[codebytere]

not ok 1026 chromium feature focus handling "before each" hook for "moves focus to the next focusable item"
  ReferenceError: emittedOnce is not defined
      at Context.beforeEach (/home/builduser/project/src/electron/spec/chromium-spec.js:1422:28)
      at processImmediate (timers.js:632:19)

is failing across several platforms, and is thus i believe consequential of this PR.

[summeroff]

Failed test is trying to use emittedOnce without including it.
Something like const { emittedOnce } = require('./events-helpers') probably can help. But I am not sure it should be fixed in this feature PR and not small fix PR that will be merged in master a lot faster.

Change what added test with emittedOnce was merged into master just 18 hours ago. So my PR can be one of the first that catches it.

[zcbenz]

The CI is broken on master branch, I also see the failed test in other unrelated PRs.

[summeroff]

For failed tests on 'ci/circleci: mas-testing-tests' run.
UPD:
3 of them will be dealt in PR #15987.

And one with timeout on getAllWebContents probably just some slowdown on host.

[release-clerk]

Release Notes Persisted

Added support for multiple browser views per BrowserWindow.

[welcome]

Congrats on merging your first pull request! 🎉🎉🎉

[0xENDER]

When I try to create a new browser view, the old one disappears.

[vmars316]

Hello & Thanks ,
Can someone aim me at an Electron browserview simple example Browser ?
Thanks for your Help...

[rumkin]

BrowserView couldn't be detached from BrowserWindow and added to another BrowserWindow. The old window still has a reference to the view in its TopLevelWindow::browser_views_ map. Filed it as a separate issue #26975.