Mac/iOS NuGet pack script (microsoft#1198)

* Update Podfile.lock

* Make publish overrides debug-compatible

If we want to use the nuget pack script to build debug configuration for sideloading, then we want optimization off and want more debug info.

* Initial nuget_pack.sh

First working version, based on refactored FUA script.  -p option is currently a no-op, but -d option builds Debug as advertised.

* Use absolute paths for xcode_select_current_version.sh

Script behavior should not depend on $PATH.

* Update Podfile.lock

* Add prerequisite tasks

- Add do_prerequisites function that does yarn/gem/pod steps to bootstrap environment enough to build the native libraries
- Add git_clean function and a third -c level since this is a pretty common troubleshooting step
- Add special handling of the (now common) pushd/popd shell builtins, to suppress their normal output while not suppressing the logging of the command itself
- Rename print_error to log_error for consistency with log_action
- Use empty/nonempty as the boolean states for bash vars 'prerequisites' and 'debug'

* Rename script to nuget_pack_apple.sh

nuget_pack.sh works for FUA, but FURN includes platforms beyond Apple, so we should be more specific.

* Escape backticks

We don't actually want to run `pod install` when printing this message.

* podfile locks

Co-authored-by: Saad Najmi <sanajmi@microsoft.com>

Author: chripear

.ado/scripts/xcode_select_current_version.sh

@@ -7,4 +7,4 @@ else
 fi
 
 echo "Running command: sudo xcode-select --switch $XCODE_PATH"
-sudo xcode-select --switch "$XCODE_PATH"
+/usr/bin/sudo /usr/bin/xcode-select --switch "$XCODE_PATH"

.ado/xcconfig/publish_overrides.xcconfig

@@ -1,10 +1,10 @@
 // For publish builds, only provide line tables for symbolizing crashes
-CLANG_DEBUG_INFORMATION_LEVEL=line-tables-only
+CLANG_DEBUG_INFORMATION_LEVEL[config=Release]=line-tables-only
 // The following build setting caused build errors, so it is commented out and placed in every podspec instead
 // OTHER_SWIFT_FLAGS=-gline-tables-only
 
 // Optimize for size in publish builds
-SWIFT_OPTIMIZATION_LEVEL=-Osize
+SWIFT_OPTIMIZATION_LEVEL[config=Release]=-Osize
 
 // Build for all architectures, not just the active one
 ONLY_ACTIVE_ARCH=NO