Add missing Complex#to_c
Use pathname.rb as MRI does and restore our native optimizations

* Pathname is a hybrid library both in MRI and JRuby.
* The JRuby native part should match MRI's native part.
* The Ruby part should be identical so it can be easily merged.
Stop excluding passing tests for Pathname
[Truffle] Exclude some backtrace entries we don't want.
[Truffle] Don't try to convert exceptions that go all the way to the top level into Ruby backtraces.
[Truffle] Tidy up how internal exceptions are reported.
[Truffle] Quick hack to get STDOUT.flush.
[Truffle] Disable by default passing loop counts through blocks - pretty sure it's counterproductive.
[Truffle] Fix EOF in gets.
Reuse common call logic for attr assign.
Return correct flag.
Fail JIT for any exception during JIT.
Remove unused runtime param.
Remove unused imports.
Split "booting" flag and do not JIT during boot of runtime.
Remove some unused imports.
Catch up with rename of isBootingRuntime back to isBooting.
Improve JIT logging for target script compile.
We do this check elsewhere.
Don't deopt for "call" calls.