if re-resolve is needed instead run update and show diff

[IanButterworth]

Fixes #3789

Simplifies by calling up on the temp env, and shows the diff.

There are two status prints if this happens.

(Foo) pkg> test
     Testing Foo
     Sandbox Could not use exact versions of packages in manifest. Re-resolving dependencies
    Updating `/private/var/folders/1z/jf841bdj73bdj3vk7kc7f_3w0000gn/T/jl_BtmYKR/Project.toml`
  [5d742f6a] + CSVFiles v1.0.2
  [324d217c] + ReferenceTests v0.10.3
  [860ef19b] + StableRNGs v1.0.1
    Updating `/private/var/folders/1z/jf841bdj73bdj3vk7kc7f_3w0000gn/T/jl_BtmYKR/Manifest.toml`
  [fbe9abb3] + AWS v1.90.4
...
⌃ [b22a6f82] ↓ FFMPEG_jll v4.4.4+1 ⇒ v4.4.2+2
⌃ [0234f1f7] ↓ HDF5_jll v1.14.2+1 ⇒ v1.12.2+2
  [e33a78d0] - Hwloc_jll v2.10.0+0
  [7cb0a576] - MPICH_jll v4.1.2+1
  [f1f71cc9] - MPItrampoline_jll v5.3.1+1
⌅ [aabc7e14] + MariaDB_Connector_C_jll v3.1.12+0
  [9237b28f] - MicrosoftMPI_jll v10.1.4+1
  [fe0851c0] - OpenMPI_jll v5.0.2+0
⌅ [458c3c95] ↓ OpenSSL_jll v3.0.13+0 ⇒ v1.1.23+0
  [32165bc3] - PMIx_jll v4.2.7+0
  [477f73a3] - libaec_jll v1.0.6+1
  [1080aeaf] - libevent_jll v2.1.13+1
  [a9144af2] + libsodium_jll v1.0.20+0
  [eb928a42] - prrte_jll v3.0.2+0
        Info Packages marked with ⌃ and ⌅ have new versions available. Those with ⌃ may be upgradable, but those with ⌅ are restricted by compatibility constraints from upgrading. To see why use `status --outdated -m`
     Sandbox Successfully re-resolved
      Status `/private/var/folders/1z/jf841bdj73bdj3vk7kc7f_3w0000gn/T/jl_BtmYKR/Project.toml`
  [5d742f6a] CSVFiles v1.0.2
...

[DilumAluthge]

Makes sense to me. Though, it seems strange to me that we don't have another way of printing a status diff (apart from Pkg.up), right?

[IanButterworth]

We do, you can feed the old env into ctx.env.old, then call status(mode:diff) or something like that, but the diff actually seems more likely to be minimal with this approach of using up rather than stripping out the manifest then calling resolve, I feel.