Feature request: allow escaping backticks in string literals

[diegommm]

Description

Allow simple escaping of backticks in string literals using backticks. Example expression:

let myConst = `
  This string contains a single backtick: ``
`;
someVar == myConst

Why

• Improve ergonomics
• Very simple to implement
• Backward compatible: it doesn't break anything
• Known pattern for escaping. Used e.g. in CSV (e.g. "field 1","field "" 2"), SQL ('It''s fine'), YAML ('It''s fine'), etc.
• Code generation use case:
  • Currently, every other literal can be used in code generation except for strings. With this approach, one can generate code for an expression and use strings.ReplaceAll(src, "`", "``") to interpolate a string constant. This would make generated code very performant and efficient.
  • Especially useful if: (1) the environment is a fixed struct with very few variables; (2) an expression needs to be generated and will be executed many times in a tight loop; (3) there can be one or many constant string values and adding them to the environment can be impractical or incur in performance costs.

Adding a reference PR with the implementation and tests: #820

[antonmedv]

Lets add it. I know no such things in Go. But we can add in Expr those.