Port member initialization from constructor to declaration (C++11)

Using `clang-tidy`'s `modernize-use-default-member-init` check and
manual review of the changes, and some extra manual changes that
`clang-tidy` failed to do.

Also went manually through all of `core` to find occurrences that
`clang-tidy` couldn't handle, especially all initializations done
in a constructor without using initializer lists.

core/crypto/crypto.cpp

@@ -94,9 +94,6 @@ Ref<X509Certificate> Crypto::generate_self_signed_certificate(Ref<CryptoKey> p_k
 	ERR_FAIL_V_MSG(nullptr, "generate_self_signed_certificate is not available when mbedtls module is disabled.");
 }
 
-Crypto::Crypto() {
-}
-
 /// Resource loader/saver
 
 RES ResourceFormatLoaderCrypto::load(const String &p_path, const String &p_original_path, Error *r_error, bool p_use_sub_threads, float *r_progress, bool p_no_cache) {

core/crypto/crypto.h

@@ -31,11 +31,10 @@
 #ifndef CRYPTO_H
 #define CRYPTO_H
 
-#include "core/reference.h"
-#include "core/resource.h"
-
 #include "core/io/resource_loader.h"
 #include "core/io/resource_saver.h"
+#include "core/reference.h"
+#include "core/resource.h"
 
 class CryptoKey : public Resource {
 	GDCLASS(CryptoKey, Resource);
@@ -80,7 +79,7 @@ public:
 	virtual Ref<CryptoKey> generate_rsa(int p_bytes);
 	virtual Ref<X509Certificate> generate_self_signed_certificate(Ref<CryptoKey> p_key, String p_issuer_name, String p_not_before, String p_not_after);
 
-	Crypto();
+	Crypto() {}
 };
 
 class ResourceFormatLoaderCrypto : public ResourceFormatLoader {

core/crypto/hashing_context.cpp

@@ -128,10 +128,6 @@ void HashingContext::_bind_methods() {
 	BIND_ENUM_CONSTANT(HASH_SHA256);
 }
 
-HashingContext::HashingContext() {
-	ctx = nullptr;
-}
-
 HashingContext::~HashingContext() {
 	if (ctx != nullptr)
 		_delete_ctx();

core/crypto/hashing_context.h

@@ -44,7 +44,7 @@ public:
 	};
 
 private:
-	void *ctx;
+	void *ctx = nullptr;
 	HashType type;
 
 protected:
@@ -57,7 +57,7 @@ public:
 	Error update(PackedByteArray p_chunk);
 	PackedByteArray finish();
 
-	HashingContext();
+	HashingContext() {}
 	~HashingContext();
 };