Two-dimensional array indexation

Uses
- Two-dimensional arrays
- Array size

Array elements are indexed using brackets:
 s:𝕊, Array2D(s)[ℕ.nz, ℕ.nz] : s

For literal array terms, indexation is implemented in Pharo:
 s_:𝕊, A:Array2D(s_), i1:ℕ.nz, i2:ℕ.nz, A[i1, i2] ⇒ Pharo:"A ensureArrayTerm. i1 ensureNumber. i2 ensureNumber. A index: i1 index: i2"

Example

For an array literal:
 {[[1, 4, 9], [16, 25, 36]]}[2, 1] ⇒ 16
Indices out of the range of valid indices are not rewritten:
 {[[1, 4, 9], [16, 25, 36]]}[1, 4] ⇒ {[[1, 4, 9], [16, 25, 36]]}[1, 4]