Fix broken debugger/debuggee startup handshake protocol on macOS26. (#5530)

As identified by dotnet/runtime#116545,
macOS26 have broken semaphores in case debugger and debuggee have been
signed with different team ids, currently only mentioned for iOS/iPadOS,
https://developer.apple.com/documentation/ios-ipados-release-notes/ios-ipados-26-release-notes,
but testing shows its broken for regular apps as well.

This PR adds support for a different startup handshake protocol for
debugger/debuggee using FIFO file (aka named pipes) on Apple platforms
due to limitation introduced in macOS26. All other POSIX platforms will
continue to use the semaphore based handshake protocol.

The implementation is backward compatible on Apple platforms.
Implementation will always setup semaphores to support runtimes using
semaphore protocol, but on Apple platforms it will also create the new
FIFO files, it will then spawn a separate background thread checking the
FIFO files for connections and handling the protocol. In case runtime
supports new FIFIO based protocol, background thread will handle
complete protocol and signal/wait semaphores, making the underlying
protocol transparent for the startup thread, it will always use the
semaphores. In case runtime doesn't support FIFO files, runtime will
signal/wait on the semaphores as normal coordinating with the debugger
startup thread. In the case runtime doesn't support FIFO files, the
background thread will just sit and wait on connections until canceled.
Unregister cancel out background thread in case runtime didn't support
FIFO files.

Since this fix supports both semaphores and FIFO files on Apple platform
it is compatible with old runtimes using semaphores as well as new
runtimes that supports the FIFO based handshake protocol.

In order for this change to work E2E, the debugger needs to use changes
introduced in this PR with a runtime including
dotnet/runtime#118120. Until both debugger and
debuggee have been update, debug launch on macOS26 won't work.

Names of the two new FIFO files follow the same naming pattern as we
have for existing debugger FIFO's, using suffix currently used for the
startup and continue semaphores, "st" for startup and "co" for continue,
example of full FIFO names:


/var/folders/d0/l_56x0lx6l7bbrv3pfr128xc0000gn/T/clr-debug-pipe-11462-1753451225-st

/var/folders/d0/l_56x0lx6l7bbrv3pfr128xc0000gn/T/clr-debug-pipe-11462-1753451225-co

Author: lateralusX