This allows Meson native-file [properties] to be used.
This avoids the need to call meson from a script file or have a
long command line invocation of `meson setup`
The method meson.get_native_property('prop', 'fallback') is added.
The native file can contain properties like
```
[properties]
myprop1 = 'foo'
mydir2 = 'lib/custom'
```
Then from within `meson.build`
```meson
x1 = meson.get_native_property('myprop1')
thedir = meson.get_native_property('mydir2', 'libs')
```
fallback values are optional