merge revision(s) 54cad3123a: [Backport #19004]

[Bug #19004] `Complex.polar` handles complex singular `abs` argument

	`Complex.polar` accepts Complex values as arguments for the polar form as long
	as the value of the complex has no imaginary part (ie it is 'real'). In
	`f_complex_polar` this is handled by extracting the real part of the arguments.
	However in the case `polar` is called with only a single argument, the absolute
	value (abs), then the Complex is created without applying a check on the type
	of abs, meaning it is possible to create a Complex where the real part is itself
	an instance of a Complex. This change removes the short circuit for the single
	argument case meaning the real part extraction is performed correctly
	(by f_complex_polar).

	Also adds an example to `spec/ruby/core/complex/polar_spec.rb` to check that
	the real part of a complex argument is correctly extracted and used in the
	resulting Complex real and imaginary parts.
	---
	 complex.c                            | 13 ++++++-------
	 spec/ruby/core/complex/polar_spec.rb | 16 ++++++++++++++++
	 2 files changed, 22 insertions(+), 7 deletions(-)

complex.c

@@ -694,14 +694,13 @@ nucomp_s_polar(int argc, VALUE *argv, VALUE klass)
 {
     VALUE abs, arg;
 
-    switch (rb_scan_args(argc, argv, "11", &abs, &arg)) {
-      case 1:
-	nucomp_real_check(abs);
-	return nucomp_s_new_internal(klass, abs, ZERO);
-      default:
-	nucomp_real_check(abs);
-	nucomp_real_check(arg);
-	break;
+    argc = rb_scan_args(argc, argv, "11", &abs, &arg);
+    nucomp_real_check(abs);
+    if (argc == 2) {
+        nucomp_real_check(arg);
+    }
+    else {
+        arg = ZERO;
     }
     if (RB_TYPE_P(abs, T_COMPLEX)) {
         get_dat1(abs);