Support multiline string syntax

[fourls]

Prerequisites

• This improvement has not already been suggested.
• This improvement would be generally useful, not specific to my code or setup.

Engine area

Delphi language support

Improvement description

Delphi 12 supports multiline strings using triple quotes (''') as follows:

• The closing ''' must be on a line of its own.
• The indentation of the closing ''' determines the base indentation of the entire string.
• None of the lines can be less indented than the base indentation.
• The last newline before the closing ''' is omitted.
• Any odd number of quotes can be used, to allow the inclusion of triple quotes in the string text.

For more details, see the official documentation and Marco Cantu's blog post introducing the feature.

Rationale

This is required to parse Delphi 12 code.

[zaneduffield]

Also note that the documentation is currently lacking the fact that the start and end quote delimiter doesn't need to be exactly 3 ' chars. It can be any odd number of ', so long as it is matched at the start and end.

[zaneduffield]

Sorry I just saw that was your last point in the list...

[cirras]

I'm sure this is going to be a joy to implement in the grammar...