As part of the effort to transition to using Debug Records instead of
Debug intrinsics, some API/argument changes are necessary to achieve the
desired behavior from Debug Records. This particular fix involves
passing iterators instead of instruction pointers to the SetInsertPoint
function. While this is crucial in certain areas, it may be more than
needed in others, but it does not cause any harm.

The module currently stores the target triple as a string. This means
that any code that wants to actually use the triple first has to
instantiate a Triple, which is somewhat expensive. The change in #121652
caused a moderate compile-time regression due to this. While it would be
easy enough to work around, I think that architecturally, it makes more
sense to store the parsed Triple in the module, so that it can always be
directly queried.

For this change, I've opted not to add any magic conversions between
std::string and Triple for backwards-compatibilty purses, and instead
write out needed Triple()s or str()s explicitly. This is because I think
a decent number of them should be changed to work on Triple as well, to
avoid unnecessary conversions back and forth.

The only interesting part in this patch is that the default triple is
Triple("") instead of Triple() to preserve existing behavior. The former
defaults to using the ELF object format instead of unknown object
format. We should fix that as well.

Rename the function to reflect its correct behavior and to be consistent
with `Module::getOrInsertFunction`. This is also in preparation of
adding a new `Intrinsic::getDeclaration` that will have behavior similar
to `Module::getFunction` (i.e, just lookup, no creation).

This used to be necessary to fetch the DataLayout, but isn't anymore.

I also ran `git clang-format` to get the headers in the right order for
the new location, which has changed the order of other headers in two
files.

Identified by modernize-use-bool-literals.

Explicitly pass loaded type when creating loads, in preparation
for the deprecation of these APIs.

There are still a couple of uses left.

Use of std::-style (io)streams is discouraged in the LLVM coding style
(https://llvm.org/docs/CodingStandards.html#include-iostream-is-forbidden).
Replace with a use of llvm::Twine (which uses llvm::raw_ostream behind
the scenes).

After D71320, target-specific intrinsic headers should be included.