Reapply [APInt] Enable APInt ctor assertion by default

This enables the assertion introduced in
#106524, which checks
that the value passed to the constructor is indeed a valid
N-bit signed or unsigned integer.

Places that previously violated the assertion were updated in
advance, e.g. in #80309.

It is possible to opt-out of the check and restore the previous
behavior by setting implicitTrunc=true.

-----

The buildbot failures from the previous attempt should be fixed
by a18dd29 and
e2074c6.

Author: nikic

llvm/include/llvm/ADT/APInt.h

@@ -109,7 +109,7 @@ class [[nodiscard]] APInt {
   /// \param implicitTrunc allow implicit truncation of non-zero/sign bits of
   ///                      val beyond the range of numBits
   APInt(unsigned numBits, uint64_t val, bool isSigned = false,
-        bool implicitTrunc = true)
+        bool implicitTrunc = false)
       : BitWidth(numBits) {
     if (!implicitTrunc) {
       if (isSigned) {