Package `assert_rpt_pkg` is redefined in each translation unit that includes `assertions.svh` when using UVM

[michael-platzer]

The assertions.svh header file includes the following code snippet, which defines a package on-the-fly when the macro UVM is defined:

common_cells/include/common_cells/assertions.svh

Lines 12 to 21 in 554ebbc

	`ifdef UVM
	// report assertion error with UVM if compiled
	package assert_rpt_pkg;
	import uvm_pkg::*;
	`include "uvm_macros.svh"
	function void assert_rpt(string msg);
	`uvm_error("ASSERT FAILED", msg)
	endfunction
	endpackage
	`endif

This works fine as long as this header is only included in one translation unit (repeated includes are avoided by the guard macros), but as soon as a second translation unit uses it as well, it leads to elaboration issues:

# ** Error (suppressible): ** while parsing file included at .bender/git/checkouts/common_cells-6e5a0419831bc5c6/src/exp_backoff.sv(23)
# ** at .bender/git/checkouts/common_cells-6e5a0419831bc5c6/include/common_cells/assertions.svh(14): (vlog-13389) Existing package 'assert_rpt_pkg' would be overwritten.

The most straight-forward resolution that I can think of, is to move these lines into a dedicated source file, call it assert_rpt_pkg.sv and add it to the design sources.

However, before proceeding with a PR, I would like to understand whether there is a particular rational behind the current solution that I am not aware of?

[phsauter]

@niwis do you know if there is a reason?
I think the proposed change makes sense and I don't see a downside.