Generate AST for variable path parsing/generation to handle property access edge cases in variable popover

[twschiller]

Context

• https://github.com/pixiebrix/pixiebrix-extension/pull/8637
• The current implementation has a corner case for bracketed expressions that end in ?, e.g., ["hello world?"]
• The check /[ .]/ for which accessors need brackets also needs to be fixed. Characters such as -, etc., would also necessitate brackets
• Ideally would use a JS parser, but @ is not a valid first character in identifiers

[fungairino]

For reference: https://github.com/pixiebrix/pixiebrix-extension/pull/8637/files#diff-e02574e2697ce0dc8b2fb077f7eb38285c3a7181250ea290e41e42cd23437e71R328-R329

[twschiller]

Closing as not planned