[Developer] KeymanWeb compiler generates invalid `KCCM` for CODE_CONTEXTEX when keyboard version < 10

**Describe the bug**
For keyboards where the keyboard target version is < 10, use of `context` on the left hand side of a rule generates a call to `KCCM` which was never implemented in KeymanWeb.

For keyboard version >= 10, the compiler complains that the `context` statement is not supported on the left hand side of a rule.

---

**Keyman Developer**:
- OS: any
- Keyman Developer version: 11.0