default variable values can lead to confusion

The default variable values (particularly for arrays) can be a problem. Especially if doing:

- create new array + variable: let array = []
- create second array + variable: let array = []
- oh no, there is no longer any way to rename just one of these variables (one solution would be for the default to become variable 2)

Other scenario
- create new array + variable: let array = []
- rename to good name, e.g fruits
- get first item from fruits -> array is selected by default and causes an exception if not noticed

The issue names no files or tests. Start by locating the Blockly paths for creating variables, renaming arrays, and selecting an array item; then reproduce both scenarios described in the issue. Done means repeated arrays can be distinguished and selecting an item after renaming no longer targets the wrong default or raises the reported exception.

Written by the indexing model from the issue text.