Importing an undefined var by running `using Package: abc` warns instead of erroring in 1.11

[krynju]

This used to be an important static check whether the thing we import actually exists. It used to fail the precompile, but now it only warns, so if you don't happen to inspect it you will not know about this.

julia> VERSION
v"1.10.7"

julia> using Base: aaa
ERROR: UndefVarError: `aaa` not defined

julia> import Base: asdsa
WARNING: could not import Base.asdsa into Main

julia> VERSION
v"1.11.1"

julia> using Base: aaa
WARNING: could not import Base.aaa into Main

julia> import Base: asdsa
WARNING: could not import Base.asdsa into Main

@KristofferC bisected it to 89e391bfd0615ba56e92457 which was added to fix #54954

According to Keno the previous behavior (meaning the error pre 1.11) was a bug, so if we want this validation it needs to be added in some way

This strict mechanism issue can be a solution to this in the future #54903

[adienes]

I definitely would like to see this error in both cases.

[jariji]

This is a bug & regression.