Improve crash handling

This adds a crash handler which reports a crash (if telemetry is enabled). On a
crash, this looks for `curl` (using the PATH env), and forks the process to then
call execve. This relies on a new endpoint to be setup to accept the "report".
Also, we include very little data..I figured just knowing about crashes would
be a good place to start.

A panic handler is provided, which override's Zig default handler and hooks
into the crash handler.

An `assert` function is added and hooks into the crash handler. This is
currently only used in one place (Session.zig) to demonstrate its use. In
addition to reporting a failed assert, the assert aborts execution in
ReleaseFast (as opposed to an undefined behavior with std.debug.assert).

I want to hook this into the v8 global error handler, but only after direct_v8
is merged.

Much of this is inspired by bun's code. They have their own assert (1) and
a [more sophisticated] crashHandler (2).
:

(1) beccd01647/src/bun.zig (L2987)
(2) beccd01647/src/crash_handler.zig (L198)

src/crash_handler.zig

@@ -0,0 +1,129 @@
+const std = @import("std");
+const lp = @import("lightpanda");
+const builtin = @import("builtin");
+
+const abort = std.posix.abort;
+
+// tracks how deep within a panic we're panicling
+var panic_level: usize = 0;
+
+// Locked to avoid interleaving panic messages from multiple threads.
+var panic_mutex = std.Thread.Mutex{};
+
+// overwrite's Zig default panic handler
+pub fn panic(msg: []const u8, _: ?*std.builtin.StackTrace, begin_addr: ?usize) noreturn {
+    @branchHint(.cold);
+    crash(msg, .{ .source = "global" }, begin_addr orelse @returnAddress());
+}
+
+pub noinline fn crash(
+    reason: []const u8,
+    args: anytype,
+    begin_addr: usize,
+) noreturn {
+    @branchHint(.cold);
+
+    nosuspend switch (panic_level) {
+        0 => {
+            panic_level = panic_level + 1;
+
+            {
+                panic_mutex.lock();
+                defer panic_mutex.unlock();
+
+                var writer_w = std.fs.File.stderr().writerStreaming(&.{});
+                const writer = &writer_w.interface;
+
+                writer.writeAll(
+                    \\
+                    \\Lightpanda has crashed. Please report the issue:
+                    \\https://github.com/lightpanda-io/browser/issues
+                    \\
+                ) catch abort();
+
+                writer.print("\nreason: {s}\n", .{reason}) catch abort();
+                writer.print("OS: {s}\n", .{@tagName(builtin.os.tag)}) catch abort();
+                writer.print("mode: {s}\n", .{@tagName(builtin.mode)}) catch abort();
+                writer.print("version: {s}\n", .{lp.build_config.git_commit}) catch abort();
+                inline for (@typeInfo(@TypeOf(args)).@"struct".fields) |f| {
+                    writer.writeAll(f.name ++ ": ") catch break;
+                    @import("log.zig").writeValue(.pretty, @field(args, f.name), writer) catch abort();
+                    writer.writeByte('\n') catch abort();
+                }
+
+                std.debug.dumpCurrentStackTraceToWriter(begin_addr, writer) catch abort();
+            }
+
+            report(reason) catch {};
+        },
+        1 => {
+            panic_level = 2;
+            var stderr_w = std.fs.File.stderr().writerStreaming(&.{});
+            const stderr = &stderr_w.interface;
+            stderr.writeAll("panicked during a panic. Aborting.\n") catch abort();
+        },
+        else => {},
+    };
+
+    abort();
+}
+
+fn report(reason: []const u8) !void {
+    if (@import("telemetry/telemetry.zig").isDisabled()) {
+        return;
+    }
+
+    var curl_path: [2048]u8 = undefined;
+    const curl_path_len = curlPath(&curl_path) orelse return;
+
+    var args_buffer: [4096]u8 = undefined;
+    var writer: std.Io.Writer = .fixed(&args_buffer);
+
+    try writer.print("https://crash.lightpanda.io/?v={s}&r=", .{lp.build_config.git_commit});
+    for (reason) |b| {
+        switch (b) {
+            'A'...'Z', 'a'...'z', '0'...'9', '-', '.', '_' => try writer.writeByte(b),
+            ' ' => try writer.writeByte('+'),
+            else => try writer.writeByte('!'), // some weird character, that we shouldn't have, but that'll we'll replace with a weird (bur url-safe) character
+        }
+    }
+
+    try writer.writeByte(0);
+    const url = writer.buffered();
+
+    var argv = [_:null]?[*:0]const u8{
+        curl_path[0..curl_path_len :0],
+        "-fsSL",
+        url[0 .. url.len - 1 :0],
+    };
+    std.debug.print("*{s}*\n", .{argv[2].?});
+
+    const result = std.c.fork();
+    switch (result) {
+        0 => {
+            _ = std.c.close(0);
+            _ = std.c.close(1);
+            _ = std.c.close(2);
+            _ = std.c.execve(argv[0].?, &argv, std.c.environ);
+            std.c.exit(0);
+        },
+        else => return,
+    }
+}
+
+fn curlPath(buf: []u8) ?usize {
+    const path = std.posix.getenv("PATH") orelse return null;
+    var it = std.mem.tokenizeScalar(u8, path, std.fs.path.delimiter);
+
+    var fba = std.heap.FixedBufferAllocator.init(buf);
+    const allocator = fba.allocator();
+
+    const cwd = std.fs.cwd();
+    while (it.next()) |p| {
+        defer fba.reset();
+        const full_path = std.fs.path.joinZ(allocator, &.{ p, "curl" }) catch continue;
+        cwd.accessZ(full_path, .{}) catch continue;
+        return full_path.len;
+    }
+    return null;
+}