core: FileStorage reads integers above INT_MAX into float/double without truncation

FileNode::operator double() and operator float() read an INT node via readInt()
(32-bit), truncating values above INT_MAX -- e.g. an integer 6662329666 from an
externally-produced json/yaml/xml is read back as -1927604926. The node stores
the value as int64 (operator int64_t() already reads it correctly via readLong),
so use readLong() for the floating-point conversions too. Values that fit in
int32 are unchanged (sign-extended); larger ones are now correct.

Reader side of #29363 (the writer side was #29364).

modules/core/src/persistence.cpp

@@ -2376,7 +2376,7 @@ FileNode::operator float() const
 
     if( type == INT )
     {
-        return (float)readInt(p);
+        return (float)readLong(p);
     }
     else if( type == REAL )
     {
@@ -2397,7 +2397,7 @@ FileNode::operator double() const
 
     if( type == INT )
     {
-        return (double)readInt(p);
+        return (double)readLong(p);
     }
     else if( type == REAL )
     {