build: generate vimfuncs at build time

This has a few advantages: we don't have to include the generated file in the
source tree, and using `include!()` avoids rustfmt and other tools checking the
file.

The location of the generated file can also be customized by setting `OUT_DIR`,
but cargo picks an appropriate temporary place in the target/ directory by
default.

Also set the default workspace members to the crates which have tests so I don't
have to forget using `--workspace` all the time.

Author: seandewar

Cargo.toml

@@ -24,3 +24,8 @@ members = [
     "crates/vimfuncs",
     "crates/format/",
 ]
+default-members = [
+    "crates/vim9-lexer",
+    "crates/vim9-parser",
+    "crates/vim9-gen",
+]

crates/vimfuncs/build.rs

@@ -1,4 +1,4 @@
-use std::io::Write;
+use std::{env, fs::File, io::Write, path::Path};
 
 use anyhow::Result;
 
@@ -326,7 +326,8 @@ impl FuncParser {
 fn main() -> Result<()> {
     println!("cargo:rerun-if-changed=data/global_functions.txt");
 
-    let mut lib = std::fs::File::create(concat!(env!("CARGO_MANIFEST_DIR"), "/src/lib.rs"))?;
+    let out_path = Path::new(&env::var_os("OUT_DIR").unwrap()).join("generated_functions.rs");
+    let mut lib = File::create(&out_path)?;
 
     // Write our struct definitions out here:
     writeln!(