Improvements to C# analysis

The following changes in version 1.23 affect C# analysis in all applications.

New queries

Query	Tags	Purpose
Unsafe year argument for 'DateTime' constructor (`cs/unsafe-year-construction`)	reliability, date-time	Finds incorrect manipulation of `DateTime` values, which could lead to invalid dates.
Mishandling the Japanese era start date (`cs/mishandling-japanese-era`)	reliability, date-time	Finds hard-coded Japanese era start dates that could be invalid.

Query	Expected impact	Change
Dereferenced variable may be null (`cs/dereferenced-value-may-be-null`)	Fewer false positive results	More `null` checks are now taken into account, including `null` checks for `dynamic` expressions and `null` checks such as `object alwaysNull = null; if (x != alwaysNull) ...`.
Missing Dispose call on local IDisposable (`cs/local-not-disposed`)	Fewer false positive results	The query has been rewritten in order to identify more dispose patterns. For example, a local `IDisposable` that is disposed of by passing through a fluent API is no longer reported.

The new class NamespaceAccess models accesses to namespaces, for example in nameof expressions.
The data-flow library now makes it easier to specify barriers/sanitizers arising from guards by overriding the predicate isBarrierGuard/isSanitizerGuard on data-flow and taint-tracking configurations respectively.
The data-flow library has been extended with a new feature to aid debugging. Instead of specifying isSink(Node n) { any() } on a configuration to explore the possible flow from a source, it is recommended to use the new Configuration::hasPartialFlow predicate, as this gives a more complete picture of the partial flow paths from a given source. The feature is disabled by default and can be enabled for individual configurations by overriding int explorationLimit().
foreach statements where the body is guaranteed to be executed at least once, such as foreach (var x in new string[]{ "a", "b", "c" }) { ... }, are now recognized by all analyses based on the control flow graph (such as SSA, data flow and taint tracking).
Fixed the control flow graph for switch statements where the default case was not the last case. This had caused the remaining cases to be unreachable. SwitchStmt.getCase(int i) now puts the default case last.
There is now a DataFlow::localExprFlow predicate and a TaintTracking::localExprTaint predicate to make it easy to use the most common case of local data flow and taint: from one Expr to another.