add support for multiline string

[aymannadeem]

"This is a " +
    "two-line string";

currently results in the following parse tree:

 (program (string_literal) (string_literal) (string_literal) (ERROR (string_literal) (UNEXPECTED '+')) (string_literal)) 

[Tmpod]

TS should also have support for Java 15 multiline strings (with triple quotes).

[raghav-deepsource]

This doesn't appear to happen in the version used in the playground for this input:

program [0, 0] - [3, 0]
  expression_statement [0, 0] - [1, 22]
    binary_expression [0, 0] - [1, 21]
      left: string_literal [0, 0] - [0, 12]
      right: string_literal [1, 4] - [1, 21]

[stadelmanma]

Any movement on this?

This looks fixed when I pulled an updated grammar and checked the JS file. Great!