feat(fetch) AbortSignal (#2019)

* add fetch abort signal

* get aborted (still segfaults)

* bidings.zig u0 error

* still GC/memory error

* fix start crash

* fix AbortSignal fromJS

* change fromJS to obj.as

* addAbortSignalEventListenner

* handle abort types, and add tests

* fix tests

* add custom reason test

* merge 2 substring methods, use MAKE_STATIC_STRING_IMPL

* fix create AbortError and TimeoutError, move globalThis and exception creation to main thread

* fix tests and rebuild headers

* no need to check with substring reason is already an exception

* no need to check with substring reason is already an exception

* fix dumb error inverting conditions for check reason

* fix custom reason behavior

src/string_immutable.zig

@@ -1133,7 +1133,6 @@ pub fn toUTF16Alloc(allocator: std.mem.Allocator, bytes: []const u8, comptime fa
                 else => return out,
             }
         } else null;
-
         var output = output_ orelse fallback: {
             var list = try std.ArrayList(u16).initCapacity(allocator, i + 2);
             list.items.len = i;