Enable crash reporting via Swift on macOS 15

Swift 5.9 includes built in crash reporting, printing stack traces,
libraries, and registers to stdout/err.

https://www.swift.org/blog/swift-5.9-backtraces/

As (Core)Foundation is written in Swift nowadays, we get this feature
for free even in our "C++" apps, as we always link to CoreFoundation.

Our test binaries have been taught how to hook into this, so the
remaining step is to enable it via the SWIFT_BACKTRACE env var.

Pick-to: 6.9
Change-Id: I72dbd9ea934ecc3091766456509f4bd42b2bdab8
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>

coin/provisioning/qtci-macos-15-arm/06-crashreporter.sh

@@ -5,3 +5,8 @@
 set -ex
 
 defaults write com.apple.CrashReporter DialogType server
+
+# shellcheck source=../common/unix/SetEnvVar.sh
+source "${BASH_SOURCE%/*}/../common/unix/SetEnvVar.sh"
+
+SetEnvVar "SWIFT_BACKTRACE" "enable=yes,output-to=stderr,preset=medium,interactive=false"

coin/provisioning/qtci-macos-15-x86_64/06-crashreporter.sh

@@ -5,3 +5,8 @@
 set -ex
 
 defaults write com.apple.CrashReporter DialogType server
+
+# shellcheck source=../common/unix/SetEnvVar.sh
+source "${BASH_SOURCE%/*}/../common/unix/SetEnvVar.sh"
+
+SetEnvVar "SWIFT_BACKTRACE" "enable=yes,output-to=stderr,preset=medium,interactive=false"