Improvements to C/C++ analysis

The following changes in version 1.26 affect C/C++ analysis in all applications.

General improvements

Query	Tags	Purpose

Query	Expected impact	Change
Declaration hides parameter (`cpp/declaration-hides-parameter`)	Fewer false positive results	False positives involving template functions have been fixed.
Inconsistent direction of for loop (`cpp/inconsistent-loop-direction`)	Fewer false positive results	The query now accounts for intentional wrapping of an unsigned loop counter.
Overflow in uncontrolled allocation size (`cpp/uncontrolled-allocation-size`)		The precision of this query has been decreased from "high" to "medium". As a result, the query is still run but results are no longer displayed on LGTM by default.
Comparison result is always the same (`cpp/constant-comparison`)	More correct results	Bounds on expressions involving multiplication can now be determined in more cases.

The QL class Block, denoting the { ... } statement, is renamed to BlockStmt.
The models library now models many taint flows through std::array, std::vector, std::deque, std::list and std::forward_list.
The models library now models many more taint flows through std::string.
The models library now models many taint flows through std::istream and std::ostream.
The models library now models some taint flows through std::shared_ptr, std::unique_ptr, std::make_shared and std::make_unique.
The models library now models many taint flows through std::pair, std::map, std::unordered_map, std::set and std::unordered_set.
The models library now models bcopy.
The SimpleRangeAnalysis library now supports multiplications of the form e1 * e2 and x *= e2 when e1 and e2 are unsigned or constant.