Update `CurrentApplicationInfo` and add support for editing it #5848

Job	Run time
Test (nightly)	1m 47s
Build docs	44s
Test (stable)	2m 37s
Examples	2m 41s
Test (macOS)	1m 58s
Test (beta)	2m 50s
Check minimal versions	33s
Test (Windows)	4m 18s
MSRV	0s
Test (native-tls)	2m 23s
Test (no default features)	55s
Test (no cache)	2m 21s
Test (no gateway)	2m 6s
Test (unstable Discord API features)	2m 47s
Test (zlib compression)	2m 41s
Test (zstd compression)	2m 38s
Test (zlib and zstd compression)	2m 29s
Test (chrono, chrono)	49s
Test (unstable API + typesize, default unstable typesize, true)	1m 5s
Test (builder without model, builder, true)	42s
Test (unstable Discord API (no default features), unstable, true)	31s
	38m 55s

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