Add TypeVisitor.

Summary: This will be useful for e.g. checking if a type contains any
Tanys.

Reviewed By: @jwatzman

Differential Revision: D1582968
Remove TranslArgs::m_interp

Summary: It's never set.

Reviewed By: @swtaarrs

Differential Revision: D1583723
Convert arm::CodeGenerator to vasm

Reviewed By: @alexmalyshev

Differential Revision: D1581040
Color partially-typed expressions yellow.

Reviewed By: @jwatzman

Differential Revision: D1582969