Inline methods of IndexedSeqOptimized in an ad hoc way.

Just because.
Circular inlining detection and prevention.
Add New to cases of SimpleMethodBody.
Add support for passing LocalDefs through chains.

So that it becomes possible to inline a closure used two
levels of inlining (or more) from where it is declared.
Mark param defs of tailrec methods mutable only if modified.
Handle This() more like VarRef() in the optimizer.
Inline more simple methods.