[cypher] parser havenot surpportted insensitive upper/lower letters

[abasi20]

your scanner is case-insensitive, so many key word have been know as upper case:eg . func as FUNC;

to reference the sql definiton , the mathric fountion : floor(1.4) must been know as floor(1.5) rather FLOOR(1.5)

your code definition:
"MATCH" { return TokenType::KW_MATCH; }

[wey-gu]

Dear @abasi20 ,

Good catch, NebulaGraph is keyword/function case-insensitive by design, so we cannot escape keyword with case-change, instead, we could do it with `

For instance, both floor and FLOOR are valid functions, and to escape floor like:

CREATE EDGE located_in_building(`floor` int);

https://docs.nebula-graph.com.cn/3.2.0/3.ngql-guide/1.nGQL-overview/identifier-case-sensitivity/#_4