Preparation for 1.7.10 release

Cherry #10540

Backport scrubber width fix to 1-7-x

Depending on whether a ScrubberItem has text or an icon, this changeset
calculates the actual width and sizes the TouchBar items accordingly.
Previously, all ScrubberItems, regardless of their content, had a static
width of 50px.

This commit also fixes #10539.

Fix crash in custom protocols caused by bad callback exec

Fix rendering issues with Nvidia GPU on High Sierra for 1.7.x

Crankshaft RCE fix

CircleCI report testing results

* Add prerelease script

* Update CircleCI for releases

* Rerun builds

Use Squirrel.Windows --checkForUpdate (1.7.x)

This cherry-picks #10483 to fix #5057.

Bump external binaries to 1.2.2

disable flaky app.importCertificate and select-client-certificate tests

* Fix app.makeSingleInstance hanging on posix systems

Wait for the IO thread to be a thing before attempting to listen on the socket

Fixes #9880

* Move OnBrowserReady call to PreMainMessageLoopRun to account for timing issues on macOS

* Woops, how did that happen ;)

* Refactor as per @zcbenz comments

Also fix issue where we run the single instance callback *not* on the UI thread,
this apparently results in a hung process.

* Appease the linting gods

* Create watcher when message loop is ready

* spec: Add test case for app.makeSingleInstance

* Fix missing extension when saving a file without filters

Previously, when triggering the save dialog through e.g. `<a download>`
links (e.g. http://jsfiddle.net/koldev/cW7W5/), the extension was only
saved if Finder was set to show all extensions by default. We now always
display the extension to make sure that it is saved.

If we want to keep the extension hidden, we could also populate the
allowed file types array with the extension from the default filename,
but that would have interfered with how we set the filters.

* Try to make test less flaky

* Try simpler test

* Fix stdout detection

* Try longer timeout on test

Apply turbofan-fix

Arm64 builds are not built for 1.7.x

Backport fix for flickering web contents on large monitors

Fixed crash on process exit on Windows