(cpp) `1.f` is considered a floating-point literal in `a1.foo()`

**Describe the issue**
See title.

**Which language seems to have the issue?**
C++ (`cpp`)

**Are you using `highlight` or `highlightAuto`?**
`highlight`.

**Sample Code to Reproduce**
`a1.foo()`

**Expected behavior**
`a1` should be an identifier, not just `a`, followed by a `1.f` floating-point literal.
