Include .h from .inc/.inl files (NFC) (#3017)

This helps both IDEs and linting tools.

Also add some missing braces.

simulation/halsim_ws_core/src/main/native/include/WSHalProviders.h

@@ -61,6 +61,6 @@ template <typename T>
 void CreateSingleProvider(const std::string& key,
                           WSRegisterFunc webRegisterFunc);
 
-#include "WSHalProviders.inl"
-
 }  // namespace wpilibws
+
+#include "WSHalProviders.inl"

simulation/halsim_ws_core/src/main/native/include/WSHalProviders.inl

@@ -8,6 +8,10 @@
 #include <string>
 #include <utility>
 
+#include "WSHalProviders.h"
+
+namespace wpilibws {
+
 template <typename T>
 void CreateProviders(const std::string& prefix, int numChannels,
                      WSRegisterFunc webRegisterFunc) {
@@ -24,3 +28,5 @@ void CreateSingleProvider(const std::string& key,
   auto ptr = std::make_unique<T>(key, key);
   webRegisterFunc(key, std::move(ptr));
 }
+
+}  // namespace wpilibws