Its a small win, dropping the number of copies and reducing the
overhead from `quote` but enough of these could make a difference

perf(derive): Reduce the amount of generated code

For now, we are still treating `clap` as the user facing API for both
builder and derive, making this an internal change as we don't expect
this to negatively impact builder build times all that much.  We can
re-evaluate at a later time and consider having distinct top-level
crates for builder and derive.

Looking at `--timings` on my machine
- `clap` only took 0.04s to build and it happened in
  parallel to `clap_builder` codegen
- this saved 1.7s for derive build times, with `clap_builder` building
  in parallel to `syn` and `clap_builder` and `clap_derive` finishing
  around the same time.

This was discussed some at https://rust-lang.zulipchat.com/#narrow/stream/220302-wg-cli/topic/clap.20build.20times.20and.20.60clap_derive.60.3A.20a.20crazy.20idea

We are doing direct transmutes between `OsStr` and `[u8]`.
rust-lang/rust#95290 would make this natively
supported but I got tired of waitin for it.

This only saves about 1/4s off of `cargo build`.

This took 2.9 KiB off of `cargo bloat --release --example git`

This adds the ability derive additional options for the group creation.

Fixes #4574

…e example documentation was not supported, so it has been updated

docs(clap_complete): clap_complete example documentation updated with corresponding file names

doc: Clean up cfgs

refactor: Split out clap_builder for faster derive builds

perf!(lex): Build faster by removing `os_str_bytes`

feat(derive): Support `#[group]` attributes

fix(lex): Allow reporting errors for non-UTF8 longs