add meson.get_native_property for native files

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

1 files changed, 16 insertions, 0 deletions

diff --git a/docs/markdown/snippets/native_property.md b/docs/markdown/snippets/native_property.md
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index 0000000..6c49e80
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+## Native file properties
+
+As of Meson 0.53.0, the `--native-file foo.txt` can contain:
+
+* binaries
+* paths
+* properties
+
+which are defined and used the same way as in cross files.
+The `properties` are new for Meson 0.53.0, and are read like:
+
+```meson
+x = meson.get_native_property('foobar', 'foo')
+```
+
+where `foobar` is the property name, and the optional `foo` is the fallback string value.
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