Split communication/vst2.h into common and VST2

So we can reuse the generic bits for our VST3 implementation.

src/common/communication/common.cpp

@@ -0,0 +1,38 @@
+#include "common.h"
+
+#include <random>
+
+#include "../utils.h"
+
+namespace fs = boost::filesystem;
+
+/**
+ * Used for generating random identifiers.
+ */
+constexpr char alphanumeric_characters[] =
+    "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
+
+boost::filesystem::path generate_endpoint_base(const std::string& plugin_name) {
+    fs::path temp_directory = get_temporary_directory();
+
+    std::random_device random_device;
+    std::mt19937 rng(random_device());
+    fs::path candidate_endpoint;
+    do {
+        std::string random_id;
+        std::sample(
+            alphanumeric_characters,
+            alphanumeric_characters + strlen(alphanumeric_characters) - 1,
+            std::back_inserter(random_id), 8, rng);
+
+        // We'll get rid of the file descriptors immediately after accepting the
+        // sockets, so putting them inside of a subdirectory would only leave
+        // behind an empty directory
+        std::ostringstream socket_name;
+        socket_name << "yabridge-" << plugin_name << "-" << random_id;
+
+        candidate_endpoint = temp_directory / socket_name.str();
+    } while (fs::exists(candidate_endpoint));
+
+    return candidate_endpoint;
+}