formatting: parallelize check and fix (#2974)
formatting: parallelize check and fix (#2974)

The files are checked and fixed independently, so process them in parallel instead of serially. With 12 cores, this reduces the time to run check_format.py from ~27s to ~5s, with the majority of the time still spent running clang_format.

Risk Level: Low

Testing: introduced formatting errors and verified that they were caught (and fixed).

Docs Changes: N/A

Release Notes: N/A

Signed-off-by: Alex Konradi <3ee61dd7715e31b012f8edaf69177fdbdc394d59@google.com>

sebrandon1/envoy,lyft/envoy,dnoe/envoy,sebrandon1/envoy,dnoe/envoy,lizan/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy,jrajahalme/envoy,eklitzke/envoy,dnoe/envoy,lyft/envoy,jrajahalme/envoy,istio/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy-wasm,eklitzke/envoy,eklitzke/envoy,envoyproxy/envoy-wasm,istio/envoy,lyft/envoy,eklitzke/envoy,eklitzke/envoy,envoyproxy/envoy,envoyproxy/envoy,lizan/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy,lizan/envoy,istio/envoy,sebrandon1/envoy,dnoe/envoy,dnoe/envoy,sebrandon1/envoy,jrajahalme/envoy,lyft/envoy,istio/envoy,istio/envoy,jrajahalme/envoy,jrajahalme/envoy,envoyproxy/envoy,sebrandon1/envoy,istio/envoy,eklitzke/envoy,lizan/envoy,lizan/envoy,envoyproxy/envoy,lyft/envoy,envoyproxy/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy,envoyproxy/envoy,jrajahalme/envoy,istio/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy-wasm,lizan/envoy,lyft/envoy