[LLVM] Add maintainers for SandboxIR and SandboxVectorizer (#115896)

I'm currently looking through some recently added components, and
noticed that SandboxIR/SandboxVec don't have a listed maintainer. I'd
like to propose vporpo and slackito as the maintainers for this
component. vporpo is the one who originally proposed this and drives
most of the implementation effort. slackito is the second most active
contributor.

Author: nikic

llvm/Maintainers.md

@@ -66,6 +66,13 @@ [email protected] (email), [qcolombet](https://github.com/qcolombet) (G
 Florian Hahn \
 [email protected] (email), [fhahn](https://github.com/fhahn) (GitHub)
 
+#### SandboxVectorizer
+
+Vasileios Porpodas \
+[email protected] (email), [vporpo](https://github.com/vporpo) (GitHub)
+Jorge Gorbe Moya \
+[email protected] (email), [slackito](https://github.com/slackito) (GitHub)
+
 #### ScalarEvolution, IndVarSimplify
 
 Philip Reames \
@@ -319,6 +326,13 @@ [email protected] (email), [pcc](https://github.com/pcc) (GitHub)
 Lang Hames \
 [email protected] (email), [lhames](https://github.com/lhames) (GitHub)
 
+#### SandboxIR
+
+Vasileios Porpodas \
+[email protected] (email), [vporpo](https://github.com/vporpo) (GitHub)
+Jorge Gorbe Moya \
+[email protected] (email), [slackito](https://github.com/slackito) (GitHub)
+
 #### TableGen
 
 Paul C. Anagnostopoulos \