feat!(blanket_impls): impl `Diagnostic` for &T and Box<T> #880

Job	Run time
Check Wasm build	20s
Check fmt & build docs	47s
Minimal versions check (ubuntu-latest)	23s
Minimal versions check (macOS-latest)	20s
Build & Test (fancy, 1.70.0, ubuntu-latest)	49s
Minimal versions check (windows-latest)	35s
Build & Test (fancy, 1.70.0, macOS-latest)	1m 35s
Miri	4m 18s
Build & Test (fancy, 1.70.0, windows-latest)	1m 15s
Build & Test (fancy, stable, ubuntu-latest)	52s
Build & Test (fancy, stable, macOS-latest)	35s
Build & Test (fancy, stable, windows-latest)	2m 32s
Build & Test (syntect-highlighter, stable, ubuntu-latest)	1m 37s
Build & Test (syntect-highlighter, stable, macOS-latest)	57s
Build & Test (syntect-highlighter, stable, windows-latest)	1m 48s
	18m 43s

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