Instrumentation into Block IR

[ChingLongTin]

Call implementation will be after the algorithms for instrumenting functions are completed.

1. allocating optionNme
   This changed some diff tests (OpenWildcard.mls, Imports.mls, ImportMLs.mls) that imported Option themselves.
   If I allocate optionNme after checking if stageCode is enabled, it fails to link to the file.
   Is there some way to avoid changing the diff tests, or is this fine?

2. implementing I-Inst
   The current shape for Class C(n:s) includes the field names (n), but the field names are not available in Instantiation.
   The field names are used in sel. If the class is staged using I-Cls, then we can use the staged ClsLikeDefn to retrieve the symbol names, but when do we do when it isn't staged?

class A(a)
staged module B
  class C(a)
  fun f() = 
    new C(1) // ok, C is staged
    new A(1) // not ok, we don't know field names of A after instrumentation

[LPTK]

Again, I don't think this should be here and neither should "Term". This is the context meant for the user. For internal uses, one should use an internal symbol (like runtimeSymbol), not a plain name. Cc @NeilKleistGao.

[NeilKleistGao]

I think the block and the shape module would not be used explicitly by users, but users do need to write code like Term.codegen. if we remove it from the context, then users should import the term module explicitly.

[LPTK]

If some functions like this should be accessible by users, they should be in the Predef. The Predef could either re-export Term (but it's a bit weird, since most things in it are not meant to be used directly by users) or define some submodule, such as module meta with { fun codegen... }.