* Fix verifier printing to print instruction encodings consistently.
Use `FuncWriter::write_instruction` for all instructions so that
encodings are printed consistently.
* Make use-before-def errors mention the relevant value.
* When there are verifier errors, print a message at the end.
* Make verifier errors prettier.
Fix the length of the "^~~~~" to match the printed entity, and print the
error messsage on its own line.
* Clean up "test verifier" failure messages.
* Tidy the uses-value-from-itself error.
The use instruction is the same as the def instruction, so don't print
both. Also, the use instruction is already being printed at the
beginning, so don't print it again at the end.
* Fixed error reporting.
* Fixed compile time error when wasm feature is disabled.
* Fixed valid instructions not being printed in print_function_error.
* Fixed errors print_function_error not writing valid instructions after end.
* Made multiple checks non-fatal.
* verify_global_values is no longer fatal.
* Slightly better formatting of errors in pretty_verifier_error.
