verilog: fix size and signedness of array querying functions

genrtlil.cc and simplify.cc had inconsistent and slightly broken
handling of signedness for array querying functions. These functions are
defined to return a signed result. Simplify always produced an unsigned
and genrtlil always a signed 32-bit result ignoring the context.

Includes tests for the the relvant edge cases for context dependent
conversions.

tests/verilog/sign_array_query.ys

@@ -0,0 +1,52 @@
+logger -expect-no-warnings
+
+read_verilog -formal <<EOT
+module top(input clk);
+    reg [-1:-1] x;
+    reg good = 0;
+    reg signed [31:0] zero = 0;
+
+    always @(posedge clk) begin
+        case ($left(x) + zero) 36'shfffffffff: good = 1; endcase
+        assert (good);
+    end
+endmodule
+EOT
+
+prep -top top
+sim -n 3 -clock clk
+
+design -reset
+
+read_verilog -formal <<EOT
+module top(input clk);
+    reg [-1:-1] x;
+    reg good = 0;
+
+    always @(posedge clk) begin
+        case ($left(x)) 36'sh0ffffffff: good = 1; (32'h0 + $left(good)): ; endcase
+        assert (good);
+    end
+
+endmodule
+EOT
+
+prep -top top
+sim -n 3 -clock clk
+
+design -reset
+
+read_verilog -formal <<EOT
+module top(input clk);
+    reg [-1:-1] x;
+    reg good = 1;
+
+    always @(posedge clk) begin
+        case (36'sh100000000 + $left(x)) -1: good = 0; endcase
+        assert (good);
+    end
+endmodule
+EOT
+
+prep -top top
+sim -n 3 -clock clk