Replace regex package module checks with actual code checks

[IanButterworth]

Fixes #55792
Replaces #55822
Improves what #51635 was trying to do

ERROR: LoadError: `using/import Printf` outside of a Module detected. Importing a package outside of a module is not allowed during package precompilation.
Stacktrace:
  [1] error(s::String)
    @ Base ./error.jl:44
  [2] require(into::Module, mod::Symbol)
    @ Base ./loading.jl:2220
  [3] include
    @ ./Base.jl:582 [inlined]
  [4] include_package_for_output(pkg::Base.PkgId, input::String, depot_path::Vector{String}, dl_load_path::Vector{String}, load_path::Vector{String}, concrete_deps::Vector{Pair{Base.PkgId, UInt128}}, source::String)
    @ Base ./loading.jl:2822
  [5] top-level scope
    @ stdin:5
  [6] eval
    @ ./boot.jl:439 [inlined]
  [7] include_string(mapexpr::typeof(identity), mod::Module, code::String, filename::String)
    @ Base ./loading.jl:2675
  [8] include_string
    @ ./loading.jl:2685 [inlined]
  [9] exec_options(opts::Base.JLOptions)
    @ Base ./client.jl:327
 [10] _start()
    @ Base ./client.jl:558
in expression starting at /var/folders/1z/jf841bdj73bdj3vk7kc7f_3w0000gn/T/jl_zoGR1X/ImportBeforeMod.jl:1
in expression starting at stdin:5

cc. @barucden

[IanButterworth]

Perhaps the part of #51635 that this doesn't do is flag when a module is completely missing and the package has no imports.

[IanButterworth]

@JeffBezanson would you mind a second look. I added detecting a missing package module.

[giordano]

Should this PR include the tests added to #55822? Unless I'm missing it, I don't see a new test which actually catches the issue described in #55792.

[IanButterworth]

We could add that test but this is more correct by design. For a comment to be parsed as julia code and trigger an import would require quite a bigger breakage.

Though, more tests is better. So I'll add it.

[IanButterworth]

There's actually a similar check on the loading side that this now gets ahead of.. But I need to check that the error is still throwing with a nice message because this looks vague:

Test Failed at /Users/julia/.julia/scratchspaces/a66863c6-20e8-4ff4-8a62-49f30b1f605e/agent-cache/default-honeycrisp-XC9YQX9HH2.0/build/default-honeycrisp-XC9YQX9HH2-0/julialang/julia-master/julia-3c844c65d7/share/julia/test/loading.jl:865
--
  | 2024-09-20 16:26:50 EDT | Expression: #= /Users/julia/.julia/scratchspaces/a66863c6-20e8-4ff4-8a62-49f30b1f605e/agent-cache/default-honeycrisp-XC9YQX9HH2.0/build/default-honeycrisp-XC9YQX9HH2-0/julialang/julia-master/julia-3c844c65d7/share/julia/test/loading.jl:866 =# @eval using BadCase
  | 2024-09-20 16:26:50 EDT | Expected: ErrorException("package `BadCase` did not define the expected module `BadCase`, check for typos in package module name")
  | 2024-09-20 16:26:50 EDT | Thrown: ErrorException("Failed to precompile BadCase [top-level] to \"/private/var/tmp/agent-tempdirs/default-honeycrisp-XC9YQX9HH2.0/tmp/jl_eWFKxn/compiled/v1.12/jl_HYOeLk\".")
  | 2024-09-20 16:26:50 EDT | Failed to precompile BadCase [top-level] to "/private/var/tmp/agent-tempdirs/default-honeycrisp-XC9YQX9HH2.0/tmp/jl_eWFKxn/compiled/v1.12/jl_HYOeLk".
  | 2024-09-20 16:26:50 EDT | Stacktrace:
  | 2024-09-20 16:26:50 EDT | [1] error(s::String)
  | 2024-09-20 16:26:50 EDT | @ Base ./error.jl:44
  | 2024-09-20 16:26:50 EDT | [2] compilecache(pkg::Base.PkgId, path::String, internal_stderr::IO, internal_stdout::IO, keep_loaded_modules::Bool; flags::Cmd, cacheflags::Base.CacheFlags, reasons::Dict{String, Int64})