Improve CGU debug printing.

- Add more total and per-CGU measurements.
- Ensure CGUs are sorted by name before the first `debug_dump` calls,
  for deterministic output.
- Print items within CGUs in sorted-by-name order, for deterministic
  output.
- Add some assertions and comments clarifying sortedness of CGUs at
  various points.

An example, before:
```
INITIAL PARTITIONING (5 CodegenUnits, max=29, min=1, max/min=29.0):
CodegenUnit scev95ysd7g4b0z estimated size 2:
 - fn <() as std::process::Termination>::report [(External, Hidden)] [h082b15a6d07338dcE] estimated size 2

CodegenUnit 1j0frgtl72rsz24q estimated size 29:
 - fn std::rt::lang_start::<()>::{closure#0} [(External, Hidden)] [h695c7b5d6a212565E] estimated size 17
 - fn std::rt::lang_start::<()> [(External, Hidden)] [h4ca942948e9cb931E] estimated size 12

CodegenUnit 5dbzi1e5qm0d7kj2 estimated size 4:
 - fn <[closure@std::rt::lang_start<()>::{closure#0}] as std::ops::FnOnce<()>>::call_once - shim [(External, Hidden)] [h24eaa44f03b2b233E] estimated size 1
 - fn <fn() as std::ops::FnOnce<()>>::call_once - shim(fn()) [(External, Hidden)] [hf338f5339c3711acE] estimated size 1
 - fn <[closure@std::rt::lang_start<()>::{closure#0}] as std::ops::FnOnce<()>>::call_once - shim(vtable) [(External, Hidden)] [h595d414cbb7651d5E] estimated size 1
 - fn std::ptr::drop_in_place::<[closure@std::rt::lang_start<()>::{closure#0}]> - shim(None) [(External, Hidden)] [h17a19dcdb40600daE] estimated size 1

CodegenUnit 220m1mqa2mlbg7r3 estimated size 1:
 - fn main [(External, Hidden)] [hb29587cdb6db5f42E] estimated size 1

CodegenUnit 4ulbh241f7tvyn7x estimated size 6:
 - fn std::sys_common::backtrace::__rust_begin_short_backtrace::<fn(), ()> [(External, Hidden)] [h41dada2c21a1259dE] estimated size 6
```
and after:
```
INITIAL PARTITIONING (9 items, total_size=42; 5 CGUs, max_size=29, min_size=1, max_size/min_size=29.0):
- CGU[0] 1j0frgtl72rsz24q (2 items, size=29):
  - fn std::rt::lang_start::<()> [(External, Hidden)] [h4ca942948e9cb931E] (size=12)
  - fn std::rt::lang_start::<()>::{closure#0} [(External, Hidden)] [h695c7b5d6a212565E] (size=17)

- CGU[1] 220m1mqa2mlbg7r3 (1 items, size=1):
  - fn main [(External, Hidden)] [hb29587cdb6db5f42E] (size=1)

- CGU[2] 4ulbh241f7tvyn7x (1 items, size=6):
  - fn std::sys_common::backtrace::__rust_begin_short_backtrace::<fn(), ()> [(External, Hidden)] [h41dada2c21a1259dE] (size=6)

- CGU[3] 5dbzi1e5qm0d7kj2 (4 items, size=4):
  - fn <[closure@std::rt::lang_start<()>::{closure#0}] as std::ops::FnOnce<()>>::call_once - shim(vtable) [(External, Hidden)] [h595d414cbb7651d5E] (size=1)
  - fn <[closure@std::rt::lang_start<()>::{closure#0}] as std::ops::FnOnce<()>>::call_once - shim [(External, Hidden)] [h24eaa44f03b2b233E] (size=1)
  - fn <fn() as std::ops::FnOnce<()>>::call_once - shim(fn()) [(External, Hidden)] [hf338f5339c3711acE] (size=1)
  - fn std::ptr::drop_in_place::<[closure@std::rt::lang_start<()>::{closure#0}]> - shim(None) [(External, Hidden)] [h17a19dcdb40600daE] (size=1)

- CGU[4] scev95ysd7g4b0z (1 items, size=2):
  - fn <() as std::process::Termination>::report [(External, Hidden)] [h082b15a6d07338dcE] (size=2)
```

1 files changed, 1 insertions, 0 deletions

diff --git a/compiler/rustc_monomorphize/src/lib.rs b/compiler/rustc_monomorphize/src/lib.rs
index ecc50c3f664..89dadc782f2 100644
--- a/compiler/rustc_monomorphize/src/lib.rs
+++ b/compiler/rustc_monomorphize/src/lib.rs
@@ -1,4 +1,5 @@
 #![feature(array_windows)]
+#![feature(is_sorted)]
 #![recursion_limit = "256"]
 #![allow(rustc::potential_query_instability)]
 #![deny(rustc::untranslatable_diagnostic)]