Make bat::PrettyPrinter::syntaxes() iterate over new bat::Syntax struct

[Enselic]

We can't keep syntect::parsing::SyntaxReference as part of the public API, because that might prevent us from bumping to syntect 6.0.0 without also bumping bat to v2.0.0.

So introduce a new stripped down struct Syntax and return that instead. Let it be fully owned to make the API simple. It is not going to be in a hot code path anyway.

I have looked at all code of our 27 dependents but I can't find a single instance of this method being used, so this change should be safe for v1.0.0. It is only used in our own example code as far as I can tell.

For reference (mostly to my future self), here is the script I used to download the code of all dependents. Then one can grep around in the code of dependents:

#/usr/bin/env bash

# curl -L 'https://crates.io/api/v1/crates/bat/reverse_dependencies' | jq --raw-output '.versions | map(.crate) | flatten[]'
# curl -L 'https://crates.io/api/v1/crates/bat/reverse_dependencies?page=2' | jq --raw-output '.versions | map(.crate) | flatten[]'
# curl -L 'https://crates.io/api/v1/crates/bat/reverse_dependencies?page=3' | jq --raw-output '.versions | map(.crate) | flatten[]'
bat_dependents="
barberousse
borrowing_exerci
bropages
cargo-expand
download_caretaker
dsconv
dts
etrade
fix-hidden-lifetime-bug-proc_macros
gistit-cli
gistit
git-delta-lib
git-delta
gooseberry
hgrep
longboard
mdn
next-gen-proc_macros
nu_plugin_textview
partiql-rs
piqel
pmis
qcow-cli
raen
riffle
trrs
with_locals-proc_macros
"

for crate in $bat_dependents; do
    echo "Processing $crate"
    mkdir -p "$crate"
    cd "$crate"
    newest_version=$(curl -L https://crates.io/api/v1/crates/$crate | jq --raw-output .crate.newest_version)
    echo "$newest_version"
    curl -L "https://crates.io/api/v1/crates/$crate/$newest_version/download" | tar -zxf -
    cd ..

    sleep 2 # avoid throttling
done

Also see #2221

[Enselic]

Just to be clear

• We should release this (and other 1.0.0 RC changes) as the usual bat 0.x.0 bump, i.e. we should not go directly to 1.0.0
• I will update CHANGELOG.md before merge

[sharkdp]

Thank you very much. This looks good to me!

[Enselic]

For the record, here is the API diff from this PR:

% cargo public-api --diff-git-checkouts origin/master stabilize-syntaxes
Removed items from the public API
=================================
(none)

Changed items in the public API
===============================
-pub fn bat::PrettyPrinter::syntaxes(&self) -> impl Iterator<Item = &SyntaxReference>
+pub fn bat::PrettyPrinter::syntaxes(&self) -> impl Iterator<Item = Syntax> + '_

Added items to the public API
=============================
+#[non_exhaustive] pub struct bat::Syntax
+pub struct field bat::Syntax::file_extensions: Vec<String>
+pub struct field bat::Syntax::name: String