Expand free alias types when computing implied outlives-bounds

[fmease]

Supersedes #122340 (see lengthy discussions in comments).
Follow-up to #119350.

Draft status: Need to add more tests, will do later — am at conf. Also: Needs better PR descr.

r? oli-obk

[fmease]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 3095448 (30954483616bccadbc38ed56731f15772acd0126, parent: ab26b175979ee7b2cb3302dce204b99df96f7efb)

[rust-timer]

Finished benchmarking commit (3095448): comparison URL.

Overall result: ✅ improvements - no action needed

Benchmarking means the PR may be perf-sensitive. Consider adding rollup=never if this change is not fit for rolling up.

@rustbot label: -S-waiting-on-perf -perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.3%	[-0.5%, -0.2%]	8
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary -3.3%, secondary -0.6%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	1.0%	[0.3%, 2.5%]	3
Improvements ✅ (primary)	-3.3%	[-3.3%, -3.3%]	1
Improvements ✅ (secondary)	-5.4%	[-5.4%, -5.4%]	1
All ❌✅ (primary)	-3.3%	[-3.3%, -3.3%]	1

Cycles

Results (secondary 19.6%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	19.6%	[19.6%, 19.6%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

This perf run didn't have relevant results for this metric.

Bootstrap: 516.59s -> 517.566s (0.19%)
Artifact size: 401.43 MiB -> 401.44 MiB (0.00%)