Build a web-based emulator for the documentation site (#1597)

Historically we've used copy-cat to provide a web-based emulator for
running example code on our documentation site. However, copy-cat is
often out-of-date with CC:T, which means example snippets fail when you
try to run them!

This commit vendors in copy-cat (or rather an updated version of it)
into CC:T itself, allowing us to ensure the emulator is always in sync
with the mod.

While the ARCHITECTURE.md documentation goes into a little bit more
detail here, the general implementation is as follows

 - In project/src/main we implement the core of the emulator. This
   includes a basic reimplementation of some of CC's classes to work on
   the web (mostly the HTTP API and ComputerThread), and some additional
   code to expose the computers to Javascript.

 - This is all then compiled to Javascript using [TeaVM][1] (we actually
   use a [personal fork of it][2] as there's a couple of changes I've
   not upstreamed yet).

 - The Javascript side then pulls in the these compiled classes (and
   the CC ROM) and hooks them up to [cc-web-term][3] to display the
   actual computer.

 - As we're no longer pulling in copy-cat, we can simplify our bundling
   system a little - we now just compile to ESM modules directly.

[1]: https://github.com/konsoletyper/teavm
[2]: https://github.com/SquidDev/teavm/tree/squid-patches
[3]: https://github.com/squiddev-cc/cc-web-term

buildSrc/src/main/kotlin/cc-tweaked.java-convention.gradle.kts

@@ -66,6 +66,7 @@ repositories {
             includeGroup("me.shedaniel.cloth")
             includeGroup("me.shedaniel")
             includeGroup("mezz.jei")
+            includeGroup("org.teavm")
             includeModule("com.terraformersmc", "modmenu")
             includeModule("me.lucko", "fabric-permissions-api")
         }
@@ -99,7 +100,10 @@ sourceSets.all {
             check("FutureReturnValueIgnored", CheckSeverity.OFF) // Too many false positives with Netty
 
             check("NullAway", CheckSeverity.ERROR)
-            option("NullAway:AnnotatedPackages", listOf("dan200.computercraft", "net.fabricmc.fabric.api").joinToString(","))
+            option(
+                "NullAway:AnnotatedPackages",
+                listOf("dan200.computercraft", "cc.tweaked", "net.fabricmc.fabric.api").joinToString(","),
+            )
             option("NullAway:ExcludedFieldAnnotations", listOf("org.spongepowered.asm.mixin.Shadow").joinToString(","))
             option("NullAway:CastToNonNullMethod", "dan200.computercraft.core.util.Nullability.assertNonNull")
             option("NullAway:CheckOptionalEmptiness")