tests: core: Convert.gen.c: Add more cases.

Some of them fail, I'm not yet sure if these
are wrong tests of rounding errors in the
implementation.

Signed-off-by: Cyril Hrubis <metan@ucw.cz>
tests: core: Add test for Convert_Scale operations

There are few failures that are caused by slightly
incorrect rounding on upsampling but these are not fatal.

Signed-off-by: Cyril Hrubis <metan@ucw.cz>