C#: Avoid using ExceptionClass in deliberate Cartesian products

Using the class `ExceptionClass` in combination with a deliberate Cartesian
product can lead to bad join orders, for example

```
EVALUATE NONRECURSIVE RELATION:
  Completion::TriedControlFlowElement::getAThrownException_dispred#ff(int this, int result) :-
    {1} r1 = JOIN Expr::Expr::getType_dispred#ff_10#join_rhs WITH @integral_type#f ON Expr::Expr::getType_dispred#ff_10#join_rhs.<0>=@integral_type#f.<0> OUTPUT FIELDS {Expr::Expr::getType_dispred#ff_10#join_rhs.<1>}
    {1} r2 = JOIN r1 WITH @un_op#f ON r1.<0>=@un_op#f.<0> OUTPUT FIELDS {r1.<0>}
    {1} r3 = JOIN r2 WITH Stmt::TryStmt::getATriedElement#ff_1#join_rhs ON r2.<0>=Stmt::TryStmt::getATriedElement#ff_1#join_rhs.<0> OUTPUT FIELDS {r2.<0>}
    {2} r4 = JOIN r3 WITH Stmt::ExceptionClass#f CARTESIAN PRODUCT OUTPUT FIELDS {Stmt::ExceptionClass#f.<0>,r3.<0>}
    {2} r5 = JOIN r4 WITH System::SystemOverflowExceptionClass#class#f ON r4.<0>=System::SystemOverflowExceptionClass#class#f.<0> OUTPUT FIELDS {r4.<1>,r4.<0>}
```

where the CP is made with `ExceptionClass` rather than `SystemOverflowExceptionClass`
directly.

csharp/ql/src/API Abuse/DisposeNotCalledOnException.ql

@@ -23,7 +23,7 @@ import semmle.code.csharp.frameworks.System
  * Gets an exception type that may be thrown during the execution of method `m`.
  * Assumes any exception may be thrown by library types.
  */
-ExceptionClass getAThrownException(Method m) {
+Class getAThrownException(Method m) {
   m.fromLibrary() and
   result = any(SystemExceptionClass sc)
   or

csharp/ql/src/semmle/code/csharp/commons/Assertions.qll

@@ -15,7 +15,7 @@ abstract class AssertMethod extends Method {
   final Parameter getAssertedParameter() { result = this.getParameter(this.getAssertionIndex()) }
 
   /** Gets the exception being thrown if the assertion fails, if any. */
-  abstract ExceptionClass getExceptionClass();
+  abstract Class getExceptionClass();
 }
 
 /** A positive assertion method. */
@@ -122,7 +122,7 @@ class SystemDiagnosticsDebugAssertTrueMethod extends AssertTrueMethod {
 
   override int getAssertionIndex() { result = 0 }
 
-  override ExceptionClass getExceptionClass() {
+  override Class getExceptionClass() {
     // A failing assertion generates a message box, see
     // https://docs.microsoft.com/en-us/dotnet/api/system.diagnostics.debug.assert
     none()
@@ -182,7 +182,7 @@ class ForwarderAssertMethod extends AssertMethod {
 
   override int getAssertionIndex() { result = p.getPosition() }
 
-  override ExceptionClass getExceptionClass() {
+  override Class getExceptionClass() {
     result = this.getUnderlyingAssertMethod().getExceptionClass()
   }
 

csharp/ql/src/semmle/code/csharp/controlflow/internal/Completion.qll

@@ -178,6 +178,13 @@ private predicate isMatchingConstant(Expr e, boolean value) {
   )
 }
 
+private class Overflowable extends UnaryOperation {
+  Overflowable() {
+    not this instanceof UnaryBitwiseOperation and
+    this.getType() instanceof IntegralType
+  }
+}
+
 /** A control flow element that is inside a `try` block. */
 private class TriedControlFlowElement extends ControlFlowElement {
   TriedControlFlowElement() { this = any(TryStmt try).getATriedElement() }
@@ -185,20 +192,15 @@ private class TriedControlFlowElement extends ControlFlowElement {
   /**
    * Gets an exception class that is potentially thrown by this element, if any.
    */
-  ExceptionClass getAThrownException() {
-    this = any(UnaryOperation uo |
-        not uo instanceof UnaryBitwiseOperation and
-        uo.getType() instanceof IntegralType and
-        result instanceof SystemOverflowExceptionClass
-      )
+  Class getAThrownException() {
+    this instanceof Overflowable and
+    result instanceof SystemOverflowExceptionClass
     or
-    this = any(CastExpr ce |
-        ce.getType() instanceof IntegralType and
-        result instanceof SystemOverflowExceptionClass
-        or
-        invalidCastCandidate(ce) and
-        result instanceof SystemInvalidCastExceptionClass
-      )
+    this.(CastExpr).getType() instanceof IntegralType and
+    result instanceof SystemOverflowExceptionClass
+    or
+    invalidCastCandidate(this) and
+    result instanceof SystemInvalidCastExceptionClass
     or
     this instanceof Call and
     result instanceof SystemExceptionClass

csharp/ql/src/semmle/code/csharp/exprs/Expr.qll

@@ -558,7 +558,7 @@ class ThrowElement extends ControlFlowElement, DotNet::Throw, @throw_element {
   override Expr getExpr() { result = this.getChild(0) }
 
   /** Gets the type of exception being thrown. */
-  ExceptionClass getThrownExceptionType() {
+  Class getThrownExceptionType() {
     result = getExpr().getType()
     or
     // Corner case: `throw null`

csharp/ql/src/semmle/code/csharp/frameworks/test/VisualStudio.qll

@@ -89,7 +89,7 @@ class VSTestAssertClass extends Class {
 }
 
 /** The `Microsoft.VisualStudio.TestTools.UnitTesting.AssertFailedException` class. */
-class AssertFailedExceptionClass extends ExceptionClass {
+class AssertFailedExceptionClass extends Class {
   AssertFailedExceptionClass() {
     this.getNamespace() instanceof VSTestNamespace and
     this.hasName("AssertFailedException")