ENH: place native and cross files in the build directory

Use a 'meson-python-' prefix to likely avoid any possible name
collision.  As the  build directory is supposed to contain build
artefact there is no advantage in using an UNIX hidden file name for
these files, and this makes them a little bit more discoverable.

Fixes #299.

Author: dnicolodi

mesonpy/__init__.py

@@ -679,8 +679,8 @@ def __init__(  # noqa: C901
         self._build_dir = pathlib.Path(build_dir).absolute() if build_dir else (self._working_dir / 'build')
         self._editable_verbose = editable_verbose
         self._install_dir = self._working_dir / 'install'
-        self._meson_native_file = self._source_dir / '.mesonpy-native-file.ini'
-        self._meson_cross_file = self._source_dir / '.mesonpy-cross-file.ini'
+        self._meson_native_file = self._build_dir / 'meson-python-native-file.ini'
+        self._meson_cross_file = self._build_dir / 'meson-python-cross-file.ini'
         self._meson_args: MesonArgs = collections.defaultdict(list)
         self._env = os.environ.copy()
 
@@ -759,14 +759,7 @@ def __init__(  # noqa: C901
             or self._meson_native_file.read_text() != native_file_data
         )
         if native_file_mismatch:
-            try:
-                self._meson_native_file.write_text(native_file_data)
-            except OSError:
-                # if there are permission errors or something else in the source
-                # directory, put the native file in the working directory instead
-                # (this won't survive multiple calls -- Meson will have to be reconfigured)
-                self._meson_native_file = self._working_dir / '.mesonpy-native-file.ini'
-                self._meson_native_file.write_text(native_file_data)
+            self._meson_native_file.write_text(native_file_data)
 
         # Don't reconfigure if build directory doesn't have meson-private/coredata.data
         # (means something went wrong)