feat: signal handling on windows (#9129)

* start some signal handling

* ok

* work on this from friday

* ok

* ref stuff

* threadsafety

* fix the buikld

* alright

* ok

* fix posix compilation error

* header fix

* revisions

---------

Co-authored-by: Jarred Sumner <jarred@jarredsumner.com>
Co-authored-by: Zack Radisic <zack@theradisic.com>

src/string.zig

@@ -733,8 +733,10 @@ pub const String = extern struct {
     }
 
     pub inline fn utf8(self: String) []const u8 {
-        if (comptime bun.Environment.allow_assert)
+        if (comptime bun.Environment.allow_assert) {
+            std.debug.assert(self.tag == .ZigString or self.tag == .StaticZigString);
             std.debug.assert(self.canBeUTF8());
+        }
         return self.value.ZigString.slice();
     }