Can't use sizeof... to initialize struct template members

```C++
#include
template
struct InfoArray {
uint8_t Number = sizeof...(Ts);
};
```
The code above does not compile.
```text
C:\Users\vhtmf\Documents\Arduino\sketch_nov5a\sketch_nov5a.ino:4:20: error: expected ';' at end of member declaration
uint8_t Number = sizeof...(Ts);
^
C:\Users\vhtmf\Documents\Arduino\sketch_nov5a\sketch_nov5a.ino:4:26: error: expected unqualified-id before '...' token
uint8_t Number = sizeof...(Ts);
^
C:\Users\vhtmf\Documents\Arduino\sketch_nov5a\sketch_nov5a.ino:4:20: error: expected primary-expression at end of input
uint8_t Number = sizeof...(Ts);
^

exit status 1

Compilation error: expected ';' at end of member declaration
```

Start with the minimal InfoArray template in C:\Users\vhtmf\Documents\Arduino\sketch_nov5a\sketch_nov5a.ino and reproduce the reported compiler errors. Then inspect the Arduino SAM compilation toolchain's handling of C++ parameter packs; done means identifying the cause and documenting or resolving whether sizeof...(Ts) can initialize the member.

Written by the indexing model from the issue text.