[ES|QL] restore better syntax error messages

[drewdaemon]

Description

21845ad resulted in some negative changes to our syntax error messages.

The top priority is row var = 1 not in

• used to result in mismatched input '<EOF>' expecting '('
• but now says mismatched input '<EOF>' expecting LP

(the lexer lost the literal name for LP, so it just gives the symbolic name... this won't be obvious to a user).

Also, an incorrect command name generates an error with a missing element in the list

from index | project

• used to result in mismatched input 'PROJECT' expecting {'dissect', 'drop', 'enrich', 'eval', 'grok', 'keep', 'limit', 'mv_expand', 'rename', 'sort', 'stats', 'where', 'lookup'}
• but now says mismatched input 'PROJECT' expecting {, 'enrich', 'dissect', 'eval', 'grok', 'limit', 'sort', 'stats', 'where', 'lookup', 'mv_expand', 'drop', 'keep', 'rename'}

Could we restore the original behavior in these cases? Particularly, the parentheses.

[elasticsearchmachine]

Pinging @elastic/es-analytical-engine (Team:Analytics)

[elasticsearchmachine]

Pinging @elastic/kibana-esql (ES|QL-ui)