Crash reports: self-hosted Sentry instead of Backtrace, and opt-in performance timings

Crash dumps now go to the project's own Sentry server. The launcher's
out-of-process helper is unchanged; only where it posts and what it expects
back are:

- The default endpoint is the Sentry project's minidump URL. Report
  attributes travel as Sentry tags, with the release as reskate@<version>.
- An upload counts as accepted when the server answers with an event ID.
- "backtrace" is "crash_report" throughout: the namespace, files, CMake
  targets, DINGOSDK_CRASH_REPORT_URL, DINGOSDK_BUILD_CRASH_REPORT_TESTS and
  the RESKATE_CRASH_REPORT_URL override.

Performance timings are new, and off unless "Send performance timings" is
ticked in the launcher's settings (RESKATE_TRACING=1). A small tracer
(Engine/Core/Debug/trace.h) posts each finished step to Sentry as a
transaction from a background thread; the launcher and the game it starts
share one trace. Timed: the update check, the Steam download, Thunderstore
installs, the mod merge, starting the game, the launch up to the first
playable level, each level load, joining a session, fetching the identity
lists, and the time spent in each level with its average frame rate and
long frames. Turning crash reports off turns timings off too.

Extension/Multiplayer/developer_identity_fetch.cpp

@@ -1,6 +1,7 @@
 #include "developer_identity.h"
 #include "word_lists.h"
 #include "Engine/Core/Log/logging.h"
+#include "Engine/Core/Debug/trace.h"
 #include "Engine/Vfs/https_download.h"
 #include <Windows.h>
 #include <atomic>
@@ -20,8 +21,10 @@ void fetch() noexcept {
     bool ok{};
     try {
         https::Download download;
+        trace::Scope timing("backend.identity_lists", "http.client");
         const auto answer = https::get_text(std::wstring(identity_lists_url.begin(), identity_lists_url.end()), max_bytes, 10,
                                             L"ReSkate-Identity/1", &download);
+        if (!answer) timing.fail();
         if (answer) {
             auto lists = parse_identity_lists(*answer);
             server_tokens_rule = parse_server_tokens_required(*answer);