[RemoteMirror][swift-inspect] Add a command to inspect the state of the concurrency runtime.

Most of the new inspection logic is in Remote Mirror. New code in swift-inspect calls the new Remote Mirror functions and formats the resulting information for display.

Specific Remote Mirror changes:

* Add a call to check if a given metadata is an actor.
* Add calls to get information about actors and tasks.
* Add a `readObj` call to MemoryReader that combines the read and the cast, greatly simplifying code chasing pointers in the remote process.
* Add a generalized facility to the C shims that can allocate a temporary object that remains valid until at least the next call, which is used to return various temporary arrays from the new calls. Remove the existing `lastString` and `lastChunks` member variables in favor of this new facility.

Swift-inspect changes:

* Add a new dump-concurrency command.
* Add a new `ConcurrencyDumper.swift` file with the implementation. The dumper needs to do some additional work with the results from Remote Mirror to build up the task tree and this keeps it all organized.
* Extend `Inspector` to query the target's threads and fetch each thread's current task.

Concurrency runtime changes:

* Add `_swift_concurrency_debug` variables pointing to the various future adapters. Remote Mirror uses these to provide a better view of a tasks's resume pointer.

rdar://85231338

include/swift/Remote/MemoryReader.h

@@ -40,6 +40,10 @@ public:
   using ReadBytesResult =
       std::unique_ptr<const void, std::function<void(const void *)>>;
 
+  template <typename T>
+  using ReadObjResult =
+      std::unique_ptr<const T, std::function<void(const void *)>>;
+
   virtual bool queryDataLayout(DataLayoutQueryType type, void *inBuffer,
                                void *outBuffer) = 0;
 
@@ -90,6 +94,15 @@ public:
     return true;
   }
 
+  template <typename T>
+  ReadObjResult<T> readObj(RemoteAddress address) {
+    auto bytes = readBytes(address, sizeof(T));
+    auto deleter = bytes.get_deleter();
+    auto ptr = bytes.get();
+    bytes.release();
+    return ReadObjResult<T>(reinterpret_cast<const T *>(ptr), deleter);
+  }
+
   /// Attempts to read 'size' bytes from the given address in the remote process.
   ///
   /// Returns a pointer to the requested data and a function that must be called to