refactor(tvix/eval): capture entire with_stack in upvalues

This completely rewrites the handling of "dynamic upvalues" to,
instead of resolving them at thunk/closure instantiation time (which
forces some values too early), capture the entire with stack of parent
contexts if it exists.

There are a couple of things in here that could be written more
efficiently, but I'm first working through this to get to a bug
related to with + recursion and the code complexity of some of the
optimisations is distracting.

Change-Id: Ia538e06c9146e3bf8decb9adf02dd726d2c651cf
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6486
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>

tvix/eval/src/opcode.rs

@@ -125,6 +125,5 @@ pub enum OpCode {
     DataLocalIdx(StackIdx),
     DataDeferredLocal(StackIdx),
     DataUpvalueIdx(UpvalueIdx),
-    DataDynamicIdx(ConstantIdx),
-    DataDynamicAncestor(UpvalueIdx),
+    DataCaptureWith,
 }