feat(tvix/eval): teach builtins.toXML context r/8163

XmlEmitter gains a NixContext field, and `write_typed_value` extends it
with all context elements present in the passed value.

Once all serialization is done, a into_context() function returns the
collected context, so we can construct a NixString with context.

Tests for this live in tvix-glue, as we use builtins.derivation, which
is not present in the tvix-eval crate.

Fixes b/398.

Change-Id: I85feaaa17b753885f8a017a54e419ec4e602af21
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11704
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>
Autosubmit: flokli <flokli@flokli.de>
Reviewed-by: Alyssa Ross <hi@alyssa.is>

0 files changed, 0 insertions, 0 deletions