Fix platform-dependent hashing for char* and wchar_t*

Since char/wchar_t can be either signed or unsigned, its conversion to uint32_t leads to different values depending on platform.
In particular, the same string represented as char* (Latin-1; StringName direct construction) or uint32_t (UTF-8; constructed
via String) previously resulted in different hashes.

core/string/ustring.cpp

@@ -2763,12 +2763,13 @@ double String::to_float() const {
 }
 
 uint32_t String::hash(const char *p_cstr) {
+	// static_cast: avoid negative values on platforms where char is signed.
 	uint32_t hashv = 5381;
-	uint32_t c = *p_cstr++;
+	uint32_t c = static_cast<uint8_t>(*p_cstr++);
 
 	while (c) {
 		hashv = ((hashv << 5) + hashv) + c; /* hash * 33 + c */
-		c = *p_cstr++;
+		c = static_cast<uint8_t>(*p_cstr++);
 	}
 
 	return hashv;
@@ -2777,28 +2778,35 @@ uint32_t String::hash(const char *p_cstr) {
 uint32_t String::hash(const char *p_cstr, int p_len) {
 	uint32_t hashv = 5381;
 	for (int i = 0; i < p_len; i++) {
-		hashv = ((hashv << 5) + hashv) + p_cstr[i]; /* hash * 33 + c */
+		// static_cast: avoid negative values on platforms where char is signed.
+		hashv = ((hashv << 5) + hashv) + static_cast<uint8_t>(p_cstr[i]); /* hash * 33 + c */
 	}
 
 	return hashv;
 }
 
 uint32_t String::hash(const wchar_t *p_cstr, int p_len) {
+	// Avoid negative values on platforms where wchar_t is signed. Account for different sizes.
+	using wide_unsigned = std::conditional<sizeof(wchar_t) == 2, uint16_t, uint32_t>::type;
+
 	uint32_t hashv = 5381;
 	for (int i = 0; i < p_len; i++) {
-		hashv = ((hashv << 5) + hashv) + p_cstr[i]; /* hash * 33 + c */
+		hashv = ((hashv << 5) + hashv) + static_cast<wide_unsigned>(p_cstr[i]); /* hash * 33 + c */
 	}
 
 	return hashv;
 }
 
 uint32_t String::hash(const wchar_t *p_cstr) {
+	// Avoid negative values on platforms where wchar_t is signed. Account for different sizes.
+	using wide_unsigned = std::conditional<sizeof(wchar_t) == 2, uint16_t, uint32_t>::type;
+
 	uint32_t hashv = 5381;
-	uint32_t c = *p_cstr++;
+	uint32_t c = static_cast<wide_unsigned>(*p_cstr++);
 
 	while (c) {
 		hashv = ((hashv << 5) + hashv) + c; /* hash * 33 + c */
-		c = *p_cstr++;
+		c = static_cast<wide_unsigned>(*p_cstr++);
 	}
 
 	return hashv;