Identified with misc-include-cleaner.

This is a helper to avoid writing `getModule()->getDataLayout()`. I
regularly try to use this method only to remember it doesn't exist...

`getModule()->getDataLayout()` is also a common (the most common?)
reason why code has to include the Module.h header.

Reverts the above commit, as it updates a common header function and
did not update all callsites:

  https://lab.llvm.org/buildbot/#/builders/29/builds/382

This reverts commit 6481dc57612671ebe77fe9c34214fba94e1b3b27.

Uses the new InsertPosition class (added in #94226) to simplify some of
the IRBuilder interface, and removes the need to pass a BasicBlock
alongside a BasicBlock::iterator, using the fact that we can now get the
parent basic block from the iterator even if it points to the sentinel.
This patch removes the BasicBlock argument from each constructor or call
to setInsertPoint.

This has no functional effect, but later on as we look to remove the
`Instruction *InsertBefore` argument from instruction-creation
(discussed
[here](https://discourse.llvm.org/t/psa-instruction-constructors-changing-to-iterator-only-insertion/77845)),
this will simplify the process by allowing us to deprecate the
InsertPosition constructor directly and catch all the cases where we use
instructions rather than iterators.

This reverts commit b5743d4798b250506965e07ebab806a3c2d767cc.

This causes some minor compile-time impact. Revert for now, better
to do the change more gradually.

Remove the old overloads that accept KnownBits by reference, in
favor of those that return it by value.

This reverts commit 0b1d1cdb89322c277baf5221218a830195fef9d4. It causes a clang crash. Details will be posted to D153638.

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D153638

Note that getMinSignedBits has been soft-deprecated in favor of
getSignificantBits.