Add selectors for cell type properties

[KrystalDelusion]

What are the reasons/motivation for this change?

#4122 and related. Also c++ code can use the RTLIL::builtin_ff_cell_types(), but there is no corresponding method for selecting builtin ff cell types from yosys scripts.

Explain how this is achieved.

1. Add (and provide values for) more CellType properties than just is_evaluable.
2. Allow these properties to be matched with the select command.
   a. Enables e.g. calling delete y:synthesizable y:formal %u %n to delete all cells that are not synthesizable or formal

Open questions:

• Should RTLIL::builtin_ff_cell_types() be removed and RTLIL::builtin_ff_cell_types().count(cell->type) be replaced with yosys_celltypes.get_cell(cell->type)->is_builtin_ff? Reduces redundancy, but requires adding #include "kernel/celltypes.h" in many of the files.
• Should is_builtin_ff be renamed to is_sequential or something, with builtin ffs being defined as is_internal and is_sequential?
• Should RTLIL::Cell::has_memid() and RTLIL::Cell::is_mem_cell() be replaced with cell type properties?

If applicable, please suggest to reviewers how they can test the change.

Call yosys -h "-celltypes" to check the assigned cell type properties make sense.

[KrystalDelusion]

So that I don't lose them, this touches on #3913, #4638, and #4034.

Currently working on updating passes/tests/test_cell.cc to also check CellTypes::eval(), but it seems like a non-zero number of 'evaluable' cells, which don't have a CellTypes::eval() implementation, do have a ConstEval::eval() implementation. Not all ($pow and $concat for instance are missing), but definitely some (like $fa and $alu). Some have duplicate definitions, such as many of the $mux family of cells; and for double fun $bmux makes a call to RTLIL::const_bmux in both versions, but has some extra checks that are only in the ConstEval version. And then the ConstEval base case is to just call CellTypes::eval.

[KrystalDelusion]

CellTypes::eval() missing support for test_cell cell types:
$macc
$lcu
$alu
$fa

ConstEval::eval() missing support for test_cell cell types:
$bwmux

test_cell missing support for evaluable cell types:
$_MUX16_
$_MUX8_
$_MUX4_
$pmux
$bweqx
$nex
$eqx

+ partial support for $buf and $pow.

The $pmux there is interesting because it is handled in both CellTypes and ConstEval, but test_cell only includes it when doing -edges which doesn't do the normal testing, and trying to include it doesn't seem to work.

$eqx and $nex have a custom ConstEval::eval() implementation, which no longer matches the behaviour since x-prop behaviour was redefined, and $bweqx doesn't work in sat or ConstEval::eval().

Which I think puts the list for cells marked evaluable but not eval-able (for some definition of eval) as:

$macc
$lcu
$alu
$fa
$_MUX16_
$_MUX8_
$_MUX4_

Unless you use ConstEval::eval(), in which case it's:

$_MUX16_
$_MUX8_
$_MUX4_

Oh, and $macc has its own Yosys::Macc::eval(), just for fun.

EDIT: Updated the supported cells.