feat: add QuasiString NodeKind for representing quasi strings in a TemplateExpr

[sam-goodwin]

Fixes #373

Adds a new NodeKind, QuasiString, to represent the raw strings in a TemplateExpr and TaggedTemplateExpr:

const a = `quasi string ${expr}`
// parses as
new TemplateExpr(new Quasi("quasi string "), new Identifier("expr"))

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[thantos]

Missing: https://github.com/fuctionless/functionless/blob/main/src/checker.ts#L846

[sam-goodwin]

Missing: https://github.com/fuctionless/functionless/blob/main/src/checker.ts#L846

I don't understand the use-case?

[sam-goodwin]

Missing: https://github.com/fuctionless/functionless/blob/main/src/checker.ts#L846

Done