initial pass improving decl parsing error messages

- all decl tokens are given an accurate starting position
- key grammar productions return token positions to facilitate the above
- helpers for standardized parse error generation
- replaced annoying pattern-matching type argument restrictions
- moving away from dumping raw decl tokens in error messages

test/error/byte_packed.sv

+// pattern: unexpected packed range\(s\) applied to byte
+module top;
+    byte [1:0] x;
+endmodule

test/error/const_const.sv

+// pattern: const_const\.sv:3:11: Parse error: duplicate const modifier
+module top;
+    const const logic x = 1'b1;
+endmodule

test/error/decl_binop_asgn.sv

+// pattern: decl_binop_asgn\.sv:3:13: Parse error: unexpected binary assignment operator in declaration
+module top;
+    logic x += 1;
+endmodule

test/error/decl_delay_asgn.sv

+// pattern: decl_delay_asgn\.sv:3:13: Parse error: unexpected timing modifier in declaration
+module top;
+    logic x = #1 1;
+endmodule

test/error/decl_delay_asgn_init.sv

+// pattern: decl_delay_asgn_init\.sv:4:24: Parse error: unexpected timing modifier in declaration
+module top;
+    initial
+        for (integer x = #1 1; 1; x++)
+            $display("Hi!");
+endmodule

test/error/decl_delay_asgn_package.sv

+// pattern: decl_delay_asgn_package\.sv:3:13: Parse error: unexpected timing modifier in declaration
+package P;
+    logic x = #1 1;
+endpackage
+module top;
+    import P::*;
+endmodule

test/error/decl_delay_asgn_port.sv

+// pattern: decl_delay_asgn_port\.sv:3:14: Parse error: unexpected timing modifier in declaration
+module top(
+    output x = #1 1
+);
+endmodule

test/error/decl_non_blocking_asgn.sv

+// pattern: decl_non_blocking_asgn\.sv:3:13: Parse error: unexpected non-blocking assignment operator in declaration
+module top;
+    logic x <= 1;
+endmodule

test/error/enum_post_signed.sv

+// pattern: unexpected signed applied to enum
+module top;
+    enum {
+        A, B
+    } signed x;
+endmodule

test/error/instantiation_extra_comma.sv

+// pattern: instantiation_extra_comma\.sv:3:18: Parse error: expected instantiation before delimiter
+module top;
+    example a(), , b();
+endmodule

test/error/instantiation_missing_ports.sv

+// pattern: instantiation_missing_ports\.sv:3:14: Parse error: expected port connections before delimiter
+module top;
+    example a, c();
+endmodule

test/error/instantiation_no_label.sv

+// pattern: instantiation_no_label\.sv:3:13: Parse error: expected instantiation name
+module top;
+    example ();
+endmodule

test/error/instantiation_no_module.sv

+// pattern: instantiation_no_module\.sv:3:5: Parse error: expected module or interface name at beginning of instantiation list
+module top;
+    , ();
+endmodule

test/error/instantiation_not_ports.sv

+// pattern: instantiation_not_ports\.sv:3:15: Parse error: expected port connections
+module top;
+    example a b, c();
+endmodule

test/error/instantiation_not_range.sv

+// pattern: instantiation_not_range\.sv:3:15: Parse error: expected instantiation dimensions
+module top;
+    example a b();
+endmodule

test/error/instantiation_trailing_comma.sv

+// pattern: instantiation_trailing_comma\.sv:3:16: Parse error: unexpected end of instantiation list
+module top;
+    example a(), ;
+endmodule

test/error/run_on_decl_item.sv

+// pattern: run_on_decl_item.sv:3:16: Parse error: unexpected comma-separated declarations
+module top;
+    integer x, byte y;
+endmodule

test/error/run_on_decl_stmt.sv

+// pattern: run_on_decl_stmt.sv:4:20: Parse error: unexpected comma-separated declarations
+module top;
+    initial begin
+        integer x, byte y;
+    end
+endmodule

test/error/string_packed.sv

+// pattern: unexpected packed range\(s\) applied to string
+module top;
+    string [1:0] x;
+endmodule

test/error/string_signed.sv

+// pattern: unexpected signed applied to string
+module top;
+    string signed x;
+endmodule

test/error/typeof_packed.sv

+// pattern: unexpected packed range\(s\) applied to type\(y\)
+module top;
+    logic y;
+    var type(y) [1:0] x;
+endmodule

test/error/typeof_signed.sv

+// pattern: unexpected signed applied to type\(y\)
+module top;
+    logic y;
+    var type(y) signed x;
+endmodule

test/error/var_var.sv

+// pattern: var_var\.sv:3:9: Parse error: duplicate var modifier
+module top;
+    var var x = 1'b1;
+endmodule