Changes

Some builders.py cleaning.

NFC. Better names, more logs.

NFC. Changed getLntSchedulers() to follow the code style of the rest of the file.

[InstrProfiling] Use ELF section groups for counters, data and values

__start_/__stop_ references retain C identifier name sections such as
__llvm_prf_*. Putting these into a section group disables this logic.

The ELF section group semantics ensures that group members are retained
or discarded as a unit. When a function symbol is discarded, this allows
allows linker to discard counters, data and values associated with that
function symbol as well.

Note that `noduplicates` COMDAT is lowered to zero-flag section group in
ELF. We only set this for functions that aren't already in a COMDAT and
for those that don't have available_externally linkage since we already
use regular COMDAT groups for those.

Differential Revision: https://reviews.llvm.org/D96757

[mlir] Add simple jupyter kernel

Simple jupyter kernel using mlir-opt and reproducer to run passes.
Useful for local experimentation & generating examples. The export to
markdown from here is not immediately useful nor did I define a
CodeMirror synax to make the HTML output prettier. It only supports one
level of history (e.g., `_`) as I was mostly using with expanding a
pipeline one pass at a time and so was all I needed.

I placed this in utils directory next to editor & debugger utils.

Differential Revision: https://reviews.llvm.org/D95742