[llvm][TableGen][Jupyter] Add configurable default reset behaviour

Often you are doing one of 2 things:
* Building a larger example from many small cells.
* Showing many small isolated examples.

Th

[llvm][TableGen][Jupyter] Add configurable default reset behaviour

Often you are doing one of 2 things:
* Building a larger example from many small cells.
* Showing many small isolated examples.

The default so far has followed iPython, where cells are connected
by default (in its case, the interpreter state backing them sticks
around).

This change adds a new magic `%config` where you can change the setting
`cellreset` to change that behaviour (this is currently the only setting).

Also added is a `%noreset` magic so that along with `%reset` you can
override the default for one particular cell.

The default is equivalent to `%config cellreset off`. If you then
wanted to reset in a cell, you can just do %reset to override it.

(this is what the current notebooks do)

If you instead do `%config cellreset on`, cells always reset and
you can choose not to using `%noreset`.

The setting is named `cellreset` not `reset` to differentiate it
a bit more from the one off command `reset`.

The demo notebook has been updated with examples of this in action.

Reviewed By: awarzynski

Differential Revision: https://reviews.llvm.org/D149055

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[LLVM][TableGen] Support combined cells in jupyter kernel

This changes the default mode to cache the code blocks we're
asked to compile until we see the new `%reset` magic to clear that cache.

This

[LLVM][TableGen] Support combined cells in jupyter kernel

This changes the default mode to cache the code blocks we're
asked to compile until we see the new `%reset` magic to clear that cache.

This means that if you run several cells in sequence, at the end you're
compiling the code from all the cells at once.

This emulates what the ipython kernel does where it uses a persistent
interpreter state by default.

`%reset` will only be acted on when it's in the cell we're asked to run
(the newest code).

`%args` we will use the most recent value we have cached.

The example notebook has been updated to explain that.

Depends on D132378

Reviewed By: jpienaar

Differential Revision: https://reviews.llvm.org/D132646

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[LLVM][TableGen] Add jupyter kernel for llvm-tblgen

This is based on the MLIR opt kernel:
https://github.com/llvm/llvm-project/tree/main/mlir/utils/jupyter

The inent of this is to enable experiment

[LLVM][TableGen] Add jupyter kernel for llvm-tblgen

This is based on the MLIR opt kernel:
https://github.com/llvm/llvm-project/tree/main/mlir/utils/jupyter

The inent of this is to enable experimentation and the creation
of interactive tutorials for the basics of tablegen.

Noteable changes from that:
* Removed the codemirror mode settings since those won't exist
for tablegen.
* Added "%args" "magic" to control arguments sent to llvm-tblgen.

(magics are directives, see
https://ipython.readthedocs.io/en/stable/interactive/magics.html)

For example the following:
```
%args --print-detailed-records
class Stuff {}

def water_bottle : Stuff {}
```
Produces:
```
DETAILED RECORDS for file -

-------------------- Global Variables (0) --------------------

-------------------- Classes (1) --------------------

Stuff |<stdin>:1|
Template args: (none)
Superclasses: (none)
Fields: (none)

-------------------- Records (1) --------------------

water_bottle |<stdin>:3|
Superclasses: Stuff
Fields: (none)
```

Reviewed By: jpienaar, awarzynski

Differential Revision: https://reviews.llvm.org/D132378

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