Add missing high-level stable_mir::generics_of fn

[spastorino]

We forgot to add this function in #115092, as we have done on #115084 and other high level APIs.

At some point I think we should re-organize the structure of the code but this is what we have for now.

r? @compiler-errors
Would have assigned @oli-obk but he is still on vacations

[rustbot]

This PR changes Stable MIR

cc @oli-obk, @celinval, @spastorino

[compiler-errors]

@bors r+ rollup

[bors]

📌 Commit 3dd1c6b has been approved by compiler-errors

It is now in the queue for this repository.

[bors]

⌛ Testing commit 3dd1c6b with merge c503527...

[bors]

☀️ Test successful - checks-actions
Approved by: compiler-errors
Pushing c503527 to master...

[rust-timer]

Finished benchmarking commit (c503527): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.9%	[-3.3%, -2.4%]	2
All ❌✅ (primary)	-	-	0

Cycles

This benchmark run did not return any relevant results for this metric.

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 632.821s -> 631.447s (-0.22%)
Artifact size: 315.71 MiB -> 315.65 MiB (-0.02%)