This PR add supports for module variables and function. The module
variables are added as global variables but their scope is set to
module instead of compile unit. The scope of function declared inside
a module is also set accordingly.

After this patch, a module variable could be evaluated in the GDB as
`p helper::gli` where helper is name of the module and gli is the name
of the variable. A future patch will add the import module functionality
which will remove the need to prefix the name with helper::.

The line number where is module is declared is a best guess at the
moment as this information is not part of the GlobalOp.

Following changes were done.

1. Remove MLIR changes as they have been moved to separate PR.

2. Replace std::map with llvm::StringMap

3. Use a direct for loop instead of module.walk.

1. Skip variables if module list is empty.

2. Add a missing line at the end of a file.

This address one of the review comments.

Fixed nits and move IR tests to Integration folder.

Add test files that work on fir and test individual passes. Remove the
fortran testcase.