Fix VariantWriter overflow on 64-bit int

Integers in Godot are signed 64-bit ints (int64_t), but var2str used
int behind the scenes and would thus overflow after 2^31.

Also properly documented the actual bounds of int and the behaviour
when overflowing them.

core/variant_parser.cpp

@@ -1597,7 +1597,7 @@ Error VariantWriter::write(const Variant &p_variant, StoreStringFunc p_store_str
 		} break;
 		case Variant::INT: {
 
-			p_store_string_func(p_store_string_ud, itos(p_variant.operator int()));
+			p_store_string_func(p_store_string_ud, itos(p_variant.operator int64_t()));
 		} break;
 		case Variant::REAL: {
 

doc/classes/@GDScript.xml

@@ -811,7 +811,7 @@
 			<description>
 				Random range, any floating point value between [code]from[/code] and [code]to[/code].
 				[codeblock]
-				prints(rand_range(0, 1), rand_range(0, 1)) # prints 0.135591 0.405263
+				prints(rand_range(0, 1), rand_range(0, 1)) # prints e.g. 0.135591 0.405263
 				[/codeblock]
 			</description>
 		</method>
@@ -830,7 +830,7 @@
 			<description>
 				Returns a random floating point value on the interval [code][0, 1][/code].
 				[codeblock]
-				randf() # returns 0.375671
+				randf() # returns e.g. 0.375671
 				[/codeblock]
 			</description>
 		</method>
@@ -838,11 +838,12 @@
 			<return type="int">
 			</return>
 			<description>
-				Returns a random 32 bit integer. Use remainder to obtain a random value in the interval [code][0, N][/code] (where N is smaller than 2^32 -1).
+				Returns a random unsigned 32 bit integer. Use remainder to obtain a random value in the interval [code][0, N][/code] (where N is smaller than 2^32 -1).
 				[codeblock]
-				randi() % 20      # returns random number between 0 and 19
+				randi()           # returns random integer between 0 and 2^32 - 1
-				randi() % 100     # returns random number between 0 and 99
+				randi() % 20      # returns random integer between 0 and 19
-				randi() % 100 + 1 # returns random number between 1 and 100
+				randi() % 100     # returns random integer between 0 and 99
+				randi() % 100 + 1 # returns random integer between 1 and 100
 				[/codeblock]
 			</description>
 		</method>

doc/classes/int.xml

@@ -4,7 +4,21 @@
 		Integer built-in type.
 	</brief_description>
 	<description>
-		Integer built-in type.
+		Signed 64-bit integer type.
+		It can take values in the interval [code][-2^63, 2^63 - 1][/code], i.e. [code][-9223372036854775808, 9223372036854775807][/code]. Exceeding those bounds will wrap around.
+		[code]int[/code] is a [Variant] type, and will thus be used when assigning an integer value to a [Variant]. It can also be enforced with the [code]: int[/code] type hint.
+		[codeblock]
+		var my_variant = 0    # int, value 0
+		my_variant += 4.2     # float, value 4.2
+		var my_int: int = 1   # int, value 1
+		my_int = 4.2          # int, value 4, the right value is implicitly cast to int
+		my_int = int("6.7")   # int, value 6, the String is explicitly cast with [method int]
+
+		var max_int = 9223372036854775807
+		print(max_int)        # 9223372036854775807, OK
+		max_int += 1
+		print(max_int)        # -9223372036854775808, we overflowed and wrapped around
+		[/codeblock]
 	</description>
 	<tutorials>
 	</tutorials>