Rework exception handling in the VM (#10544)

* Rework exception handling in the VM

Make the safepoint handling more precise and less forgiving.
The new code is clearer and more commented.
Perform cleanup on `return`.
The no-exception-thrown case in a try block should be slightly faster
since we don't parse the whole set of exceptions every time.
More tests.

* Fix silly error that broke a few tests

* Testament doesn't like files having the same name

* Remove test case that failed compilation to js

tests/exception/texceptions.nim

@@ -74,3 +74,54 @@ block: #10417
       moo()
 
   doAssert(bar == 1)
+
+# Make sure the VM handles the exceptions correctly
+block:
+  proc fun1(): seq[int] =
+    try:
+      try:
+        raise newException(ValueError, "xx")
+      except:
+        doAssert("xx" == getCurrentExceptionMsg())
+        raise newException(KeyError, "yy")
+    except:
+      doAssert("yy" == getCurrentExceptionMsg())
+      result.add(1212)
+    try:
+      try:
+        raise newException(AssertionError, "a")
+      finally:
+        result.add(42)
+    except AssertionError:
+      result.add(99)
+    finally:
+      result.add(10)
+    result.add(4)
+    result.add(0)
+    try:
+      result.add(1)
+    except KeyError:
+      result.add(-1)
+    except ValueError:
+      result.add(-1)
+    except IndexError:
+      result.add(2)
+    except:
+      result.add(3)
+
+    try:
+      try:
+        result.add(1)
+        return
+      except:
+        result.add(-1)
+      finally:
+        result.add(2)
+    except KeyError:
+      doAssert(false)
+    finally:
+      result.add(3)
+
+  let x1 = fun1()
+  const x2 = fun1()
+  doAssert(x1 == x2)