Calculate used variable names better in buildRule

[ehildenb]

This PR does several things:

• Moves splitConfigAndConstraint to inside CTerm, so now there are no dependencies of cterm.py on kastManip.py.
• Renames variables in buildRule, and renames method to build_rule.
• Lifts build_rule to operate over CTerm, instead of over KInner.
• Adds a test where build_rule is producing variable names in the rule which cause the frontend to emit warnings.
• Fixes bug where build_rule is naming variables poorly.
• Adds a method with_constraint to CTerm for easily making new CTerm with an added constraint.
• Removes an old test of build_rule that becomes redundant with the added tests here.
• Moves the test_configuration.py tests into unit tests under test_kastManip.py so they don't build definitions every time (they don't need to).

The main change to buildRule is that if you have a rule:

    rule <k> K_CELL ... </k> <mem> MEM => MEM' </mem>

It will now realize that K_CELL should be anonymous, and rename it to _K_CELL before feeding it to the frontend. This is to avoid a bunch of frontend warnings.

[tothtamas28]

I'd call it add_constraint instead. To me, with_constraint suggests "take the configuration, and couple it with the constraint provided."

Suggested change

	def with_constraint(self, new_constraint: KInner) -> 'CTerm':
	return CTerm(mlAnd([self.config, new_constraint] + list(self.constraints), Sorts.GENERATED_TOP_CELL))
	def add_constraint(self, constraint: KInner) -> 'CTerm':
	return CTerm(mlAnd((self.config, constraint) + self.constraints, Sorts.GENERATED_TOP_CELL))

[ehildenb]

Done.

[tothtamas28]

As a first step, I'd just move this to cterm.py. Later, when we are ready to eliminate calls to the function, e.g. by replacing

config, constraint = split_config_and_constraints(term)

by

config, *constraints = Cterm(term)
constraint = mlAnd(constraints)

we can make it a private static method.

[ehildenb]

Done.

[nishantjr]

Looks good.