Use correct accuracy for the RR domain

We use two extra guard digits from the maximum precision of all coefficients.

Previously:

In [1]: simplify(1e-14*I)
Out[1]: 0

Now:

In [1]: simplify(1e-14*I)
Out[1]: 1.0e-14⋅ⅈ

Fixes sympy#9398

sympy/polys/constructor.py

@@ -6,6 +6,7 @@
 from sympy.polys.polyoptions import build_options
 from sympy.polys.polyerrors import GeneratorsNeeded
 from sympy.polys.domains import ZZ, QQ, RR, EX
+from sympy.polys.domains.realfield import RealField
 from sympy.utilities import public
 from sympy.core import sympify
 
@@ -44,7 +45,8 @@ def _construct_simple(coeffs, opt):
         domain, result = _construct_algebraic(coeffs, opt)
     else:
         if reals:
-            domain = RR
+            max_prec = max([c._prec for c in coeffs])
+            domain = RealField(prec=max_prec+2)
         else:
             if opt.field or rationals:
                 domain = QQ