Add rspfile support to RuleBuilder

Allow RuleBuilderCommands to use an rspfile with FlagWithRspFileInputList.
This requires being more careful with ninja escaping, as the rspfile
will be $out.rsp, and the value for $out may not be known yet so it
must be inserted as a ninja variable that must not be escaped.

Test: rule_builder_test.go
Change-Id: Ifa91e24a0bb8f0ceeb5c9bfa5689be2a4ff3b9cd