Adopt `ArrayRef::consume_front()` in `PrintMessage`, and convert the
loop in that function to a range for loop.

This is a part of effort to have better const correctness in TableGen
backends:


https://discourse.llvm.org/t/psa-planned-changes-to-tablegen-getallderiveddefinitions-api-potential-downstream-breakages/81089

Print assert message after the "assertion failed" message instead of
printing it as a separate note. This makes the assert failure reporting
less verbose and also more useful to see the failure message inline with
the "assertion failed" message.

When record assertions fail, print an error message with the record's
location, so it's easier to see where the record that caused the assert
to fail was instantiated. This is useful when the assert condition in a
class depends on a template parameter, so we need to know the context of
the definition to determine why the assert failed.

Also enhanced the assert.td test to check for these context messages,
and also add checks for some assert failures that were missing in the
test.

Add PrintError and family overload that accepts a print function. This
avoids constructing potentially long strings for passing into these
print functions.

Co-authored-by: Akshat Oke <Akshat.Oke@amd.com>

The keyword is intended for debugging purpose. It prints a message to
stderr.

This patch is based on code originally written by Adam Nemet, and on the
feedback received by the reviewers in
https://reviews.llvm.org/D157492.

This commits removes TableGens reliance on managed static global record state
by moving the RecordContext into the RecordKeeper. The RecordKeeper is now
treated similarly to a (LLVM|MLIR|etc)Context object and is passed to static
construction functions. This is an important step forward in removing TableGens
reliance on global state, and in a followup will allow for users that parse tablegen
to parse multiple tablegen files without worrying about Record lifetime.

Differential Revision: https://reviews.llvm.org/D125276

Differential Revision: https://reviews.llvm.org/D99275

Update the documentation.

Rework various backends that relied on the code type.

Differential Revision: https://reviews.llvm.org/D92269