refactor(rustc_middle): Substs -> GenericArg

[mdibaiee]

resolves #110793

• rename SubstsRef and InternalSubsts to GenericArgsRef<'tcx> and GenericArgs<'tcx>.
• rename variables and fields currently using substs to args.
• update the module name of ty::subst to ty::generic_args or sth. Make that module private and publicly reexport its content in the ty module.
• rename EarlyBinder::subst(_identity) to EarlyBinder::instantiate(_identity).
• types called [a-zA-Z]+Substs renamed to XArgs.
• functions containing substs now use args or generic_args (mostly the former).

However, the verb of "substituting" is still being used here and there, mostly in comments. I think that can be a separate PR as part of #110254 to change the verb to replace_generics or something similar.

[rustbot]

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[mdibaiee]

@rustbot label -S-waiting-on-review +S-waiting-on-author

[mdibaiee]

r? ghost

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[rust-timer]

Finished benchmarking commit (5767cad): comparison URL.

Overall result: ❌ regressions - no action needed

@rustbot label: -perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.3%	[0.3%, 0.4%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

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)	-3.3%	[-4.2%, -2.3%]	3
All ❌✅ (primary)	-	-	0

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)	3.5%	[1.5%, 4.6%]	7
Regressions ❌ (secondary)	5.9%	[5.9%, 5.9%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	3.5%	[1.5%, 4.6%]	7

Binary size

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

Bootstrap: 659.454s -> 657.557s (-0.29%)