core: Make converting constructors explicit where applicable

Avoids unwanted implicit conversions. Thankfully, given the large amount
of cleanup in past PRs, only this tiny amount is left over to cover.

src/core/hle/service/service.h

@@ -222,7 +222,7 @@ protected:
      * @param max_sessions Maximum number of sessions that can be
      * connected to this service at the same time.
      */
-    ServiceFramework(const char* service_name, u32 max_sessions = DefaultMaxSessions)
+    explicit ServiceFramework(const char* service_name, u32 max_sessions = DefaultMaxSessions)
         : ServiceFrameworkBase(service_name, max_sessions, Invoker) {}
 
     /// Registers handlers in the service.

src/core/loader/elf.cpp

@@ -189,7 +189,7 @@ private:
     u32 entryPoint;
 
 public:
-    ElfReader(void* ptr);
+    explicit ElfReader(void* ptr);
 
     u32 Read32(int off) const {
         return base32[off >> 2];

src/core/loader/loader.h

@@ -84,7 +84,7 @@ constexpr u32 MakeMagic(char a, char b, char c, char d) {
 /// Interface for loading an application
 class AppLoader : NonCopyable {
 public:
-    AppLoader(FileUtil::IOFile&& file) : file(std::move(file)) {}
+    explicit AppLoader(FileUtil::IOFile&& file) : file(std::move(file)) {}
     virtual ~AppLoader() {}
 
     /**

src/core/tracer/recorder.h

@@ -32,7 +32,7 @@ public:
      * Recorder constructor
      * @param initial_state Initial recorder state
      */
-    Recorder(const InitialState& initial_state);
+    explicit Recorder(const InitialState& initial_state);
 
     /// Finish recording of this Citrace and save it using the given filename.
     void Finish(const std::string& filename);