coding_guideline: Add optional flag to check invalid conversions

Generate errors for implicit conversions that may alter a value, that
covers conversions implicit conversions to narrower types, different
signal, different essential types (float -> int), ... From GCC
documentation
(https://gcc.gnu.org/onlinedocs/gcc-9.3.0/gcc/Warning-Options.html

)

"""
Warn for implicit conversions that may alter a value. This includes
conversions between real and integer, like abs (x) when x is double;
conversions between signed and unsigned, like unsigned ui = -1; and
conversions to smaller types, like sqrtf (M_PI). Do not warn for
explicit casts like abs ((int) x) and ui = (unsigned) -1, or if the
value is not changed by the conversion like in abs (2.0). Warnings
about conversions between signed and unsigned integers can be disabled
by using -Wno-sign-conversion.

For C++, also warn for confusing overload resolution for user-defined
conversions; and conversions that never use a type conversion
operator: conversions to void, the same type, a base class or a
reference to them. Warnings about conversions between signed and
unsigned integers are disabled by default in C++ unless
-Wsign-conversion is explicitly enabled.
"""

This partially cover rules: 10.4, 10.5, 10.6, 10.7 and 10.8

Signed-off-by: Flavio Ceolin <flavio.ceolin@intel.com>