Auto-pkg-installation error should probably load Pkg

[Keno]

Here's another one of the "things behave differently after loading Pkg" issues:

julia> using BenchmarkTools
ERROR: ArgumentError: Package BenchmarkTools not found in current path.
- Run `import Pkg; Pkg.add("BenchmarkTools")` to install the BenchmarkTools package.
Stacktrace:
 [1] macro expansion
   @ ./loading.jl:2074 [inlined]
 [2] macro expansion
   @ ./lock.jl:273 [inlined]
 [3] __require(into::Module, mod::Symbol)
   @ Base ./loading.jl:2049
 [4] #invoke_in_world#3
   @ ./essentials.jl:1064 [inlined]
 [5] invoke_in_world
   @ ./essentials.jl:1061 [inlined]
 [6] require(into::Module, mod::Symbol)
   @ Base ./loading.jl:2042

(@v1.12) pkg>

julia> using BenchmarkTools
 │ Package BenchmarkTools not found, but a package named BenchmarkTools is
 │ available from a registry.
 │ Install package?
 │   (@v1.12) pkg> add BenchmarkTools
 └ (y/n/o) [y]:

Since this is an error path in the REPL, I don't see any reason for this not to try to automatically load Pkg.

[Keno]

Dup of #52090, I just searched for the wrong keyword.