* module/language/elisp/README: Document it.
* module/language/elisp/compile-tree-il.scm: Moved ensure-fluid! to runtime function.
* module/language/elisp/runtime.scm: Runtime functions to support dynamic value access.
* module/language/elisp/runtime/function-slot.scm: Defined the built-ins.
* test-suite/tests/elisp-compiler.test: Test them.