ndk: Remove and warn on trivial casts

`trivial-casts` is allowed by default as it still has some odd cases
where the lint triggers incorrectly or is difficult to fix.  For our
intents and purposes however it works just fine and prevents against
riddling the code with unnecessary - usually untyped - `as` casts.

https://doc.rust-lang.org/rustc/lints/listing/allowed-by-default.html#explanation-22

ndk/src/configuration.rs

@@ -136,7 +136,7 @@ impl Configuration {
     pub fn country(&self) -> String {
         let mut result = "  ".to_owned();
         unsafe {
-            ffi::AConfiguration_getCountry(self.ptr.as_ptr(), result.as_mut_ptr() as *mut _);
+            ffi::AConfiguration_getCountry(self.ptr.as_ptr(), result.as_mut_ptr());
         }
         result
     }
@@ -172,11 +172,11 @@ impl Configuration {
         }
     }
 
-    /// Returns the language, as a `String` of two characters, if a language is set
+    /// Returns the language, as a [`String`] of two characters, if a language is set
     pub fn language(&self) -> Option<String> {
         let mut chars = [0u8; 2];
         unsafe {
-            ffi::AConfiguration_getLanguage(self.ptr.as_ptr(), chars[..].as_mut_ptr() as *mut _);
+            ffi::AConfiguration_getLanguage(self.ptr.as_ptr(), chars.as_mut_ptr());
         }
         if chars[0] == 0 {
             None

ndk/src/lib.rs

@@ -13,7 +13,7 @@
     feature = "native_app_glue",
     doc = "  * `native_app_glue`'s `AndroidApp`, in the `android_app` module"
 )]
-#![warn(missing_debug_implementations)]
+#![warn(missing_debug_implementations, trivial_casts)]
 
 pub mod asset;
 pub mod bitmap;