parser: move code generation into a test

[djc]

Move the pest parser code generation step into a test. Makes it so that downstream users don't have to spend the time compiling some of the dependencies (in this case, pest_meta and its sha-1 dependency).

Inspired by steveklabnik/semver-parser#50. It's not as big an improvement here because we still depend on serde's Serialize and Deserialize macros, but seems like a nice improvement anyway.

[sunli829]

LGTM 🙂

[sunli829]

@djc An absolute path will be generated here, do you know how to solve it? 😁

async-graphql/parser/src/parse/generated.rs

Line 8 in ad05baf

include_str!("/Users/sunli/work/async-graphql/parser/src/graphql.pest");

[djc]

Ah, so I guess the pest derive macro expands the relative path to the grammar to an absolute path? I guess you can just patch up the generated code in the code generation test, by generating the same absolute path and replacing it with a relative path?

Also, what's the reason for merging this into the v4 branch? It seems semver-compatible, so could just go in v3, right?