Check FnPtr/FnDef built-in fn traits correctly with effects

[compiler-errors]

1. Teach the (old) trait solver how to handle the constness for built-in impls of the Fn* family of traits. This unfortunately doesn't support const closures just yet.
2. Fix the const_eval_select. It turns out that the where clause bounds on const_eval_select force the effect parameter for both fndefs to be true -- with effects, we will leave off any explicit where clauses and register these obligations manually.

I can elaborate on (2.) if you think it needs a better explanation!

r? fee1-dead

[rustbot]

Could not assign reviewer from: fee1-dead.
User(s) fee1-dead are either the PR author, already assigned, or on vacation, and there are no other candidates.
Use r? to specify someone else to assign.

[fee1-dead]

Thanks, r=me after addressing the nits

[compiler-errors]

@bors r=fee1-dead

[bors]

📌 Commit faea6ad has been approved by fee1-dead

It is now in the queue for this repository.

[bors]

⌛ Testing commit faea6ad with merge 3f28fe1...

[bors]

☀️ Test successful - checks-actions
Approved by: fee1-dead
Pushing 3f28fe1 to master...

[rust-timer]

Finished benchmarking commit (3f28fe1): 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)	3.3%	[3.3%, 3.3%]	1
Regressions ❌ (secondary)	1.0%	[1.0%, 1.1%]	3
Improvements ✅ (primary)	-0.8%	[-1.2%, -0.6%]	3
Improvements ✅ (secondary)	-3.6%	[-3.6%, -3.6%]	1
All ❌✅ (primary)	0.2%	[-1.2%, 3.3%]	4

Cycles

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)	0.5%	[0.5%, 0.6%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.6%	[-1.8%, -1.5%]	2
All ❌✅ (primary)	0.5%	[0.5%, 0.6%]	2

Binary size

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

Bootstrap: 674.217s -> 673.523s (-0.10%)
Artifact size: 312.46 MiB -> 312.51 MiB (0.01%)