py/parse: Add support for math module constants and float folding.

Add a new MICROPY_COMP_CONST_FLOAT feature, enabled by in mpy-cross and
when compiling with MICROPY_CONFIG_ROM_LEVEL_CORE_FEATURES.  The new
feature leverages the code of MICROPY_COMP_CONST_FOLDING to support folding
of floating point constants.

If MICROPY_COMP_MODULE_CONST is defined as well, math module constants are
made available at compile time. For example:

    _DEG_TO_GRADIANT = const(math.pi / 180)
    _INVALID_VALUE = const(math.nan)

A few corner cases had to be handled:
- The float const folding code should not fold expressions resulting into
  complex results, as the mpy parser for complex immediates has
  limitations.
- The constant generation code must distinguish between -0.0 and 0.0, which
  are different even if C consider them as ==.

This change removes previous limitations on the use of `const()`
expressions that would result in floating point number, so the test cases
of micropython/const_error have to be updated.

Additional test cases have been added to cover the new repr() code (from a
previous commit).  A few other simple test cases have been added to handle
the use of floats in `const()` expressions, but the float folding code
itself is also tested when running general float test cases, as float
expressions often get resolved at compile-time (with this change).

Signed-off-by: Yoctopuce dev <dev@yoctopuce.com>

py/emitcommon.c

@@ -25,6 +25,7 @@
  */
 
 #include <assert.h>
+#include <math.h>
 
 #include "py/emit.h"
 #include "py/nativeglue.h"
@@ -72,7 +73,21 @@ static bool strictly_equal(mp_obj_t a, mp_obj_t b) {
         }
         return true;
     } else {
-        return mp_obj_equal(a, b);
+        if (!mp_obj_equal(a, b)) {
+            return false;
+        }
+        #if MICROPY_PY_BUILTINS_FLOAT && MICROPY_COMP_CONST_FLOAT
+        if (a_type == &mp_type_float) {
+            mp_float_t a_val = mp_obj_float_get(a);
+            if (a_val == (mp_float_t)0.0) {
+                // Although 0.0 == -0.0, they are not strictly_equal and
+                // must be stored as two different constants in .mpy files
+                mp_float_t b_val = mp_obj_float_get(b);
+                return signbit(a_val) == signbit(b_val);
+            }
+        }
+        #endif
+        return true;
     }
 }