feat(tvix/eval): implement builtins.toXML

Change-Id: I009efc53a8e98f0650ae660c4decd8216e8a06e7
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7835
Reviewed-by: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI

corp/tvixbolt/Cargo.lock

@@ -289,6 +289,7 @@ dependencies = [
  "imbl-sized-chunks",
  "rand_core",
  "rand_xoshiro",
+ "serde",
  "version_check",
 ]
 
@@ -665,6 +666,7 @@ dependencies = [
  "smol_str",
  "tabwriter",
  "tvix-eval-builtin-macros",
+ "xml-rs",
 ]
 
 [[package]]
@@ -822,6 +824,12 @@ version = "0.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "712e227841d057c1ee1cd2fb22fa7e5a5461ae8e48fa2ca79ec42cfc1931183f"
 
+[[package]]
+name = "xml-rs"
+version = "0.8.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d2d7d3948613f75c98fd9328cfdcc45acc4d360655289d0a7d4ec931392200a3"
+
 [[package]]
 name = "yew"
 version = "0.19.3"