[bmordue]

Adds a set of new mutators, presets that group them, and a convenience function that returns every mutator.

New mutators

• Calls and arguments: drop_argument(), reverse_arguments(), remove_validation(), flip_named_flag(), replace_call_result(), remove_pipe_stage()
• Control flow: condition_constant(), remove_else_branch(), empty_if_body(), remove_null_guard(), keep_operand(), replace_implicit_return()
• Literals and sequences: remove_unary_minus(), integer_to_double(), double_to_integer(), numeric_replace(), seq_len_decrement(), seq_along_drop_first(), colon_start_increment(), colon_end_decrement()

New presets

function_swaps() (any/all, min/max, nrow/ncol, …), membership_operators(), operand_elision(), branch_mutations(), numeric_boundaries(), numeric_type_swaps(), sequence_mutations()

all_mutators(): Returns a flat list of every mutator, all with default arguments, for a first exploratory run. Overlapping mutators appear only once.