String concatenation in YANG model leads to syntax error

[dus7eh]

According to YANG RFC 7950 (https://datatracker.ietf.org/doc/html/rfc7950#section-6.1.3) quoted strings should be concatenated.

When parsing a YANG model with for example:

...
uses 'some_prefix:'+
     'grouping_name';
...

the following error is logged: syntax error at or before: '''

Expected behavior: yang model is parsed successfully

[olofhagsand]

There are two errors:

1. single quotes in some identifiers (eg uses above) causes errors.
2. quoted string + quoted string as noted in the error description above is not implemented for many identifiers, including uses.
   Error (1) can be fixed separately
   Error (2) is related (not same) as Can't use + symbol in the enum statement without quotes #241 and needs a rewrite of the scanner.

[olofhagsand]

Error(1) fixed by patch above.

[olofhagsand]

Error (2) patched by 9d65fb8