arrow

GH-37148: [C++] Explicitly list the integer values of the Type::type enum (#37149)

### Rationale for this change

The enum type in C++ leaves the integer values implicitly defined and let the compiler assign the values to them automatically. This means an insertion of a new entry that is not at the end, causes implementations that rely on specific values (like R) to break with confusing error messages [1].

Assigning the values explicitly can communicate that these enum entry values are relied upon and can allow a more natural ordering of the list that is different from the numeric order the entries receive.

[1] https://github.com/apache/arrow/issues/37091

### What changes are included in this PR?

 - Setting numeric values of the enum entries explicitly
 - Completing an equivalent enum on the R side 
 
### Are these changes tested?

N/A

### Are there any user-facing changes?

No.
* Closes: #37148

Authored-by: Felipe Oliveira Carvalho <felipekde@gmail.com>
Signed-off-by: Benjamin Kietzman <bengilgit@gmail.com>