Bump version number to 1.19.0 (#1637) #837

Job	Run time
Integration Tests on swiftlang/swift:nightly-focal	4m 16s
Integration Tests on swift:5.8-jammy	2m 54s
Integration Tests on swift:5.7-jammy	3m 39s
Integration Tests on swift:5.6-focal	2m 43s
Performance Tests on swiftlang/swift:nightly-focal	10m 18s
Performance Tests on swift:5.8-jammy	9m 14s
Performance Tests on swift:5.7-jammy	8m 58s
Performance Tests on swift:5.6-focal	9m 0s
License Header and Formatting Checks	2m 30s
Build and Test on swiftlang/swift:nightly-focal	5m 56s
Build and Test on swift:5.8-jammy	3m 59s
Build and Test on swift:5.7-jammy	4m 20s
Build and Test on swift:5.6-focal	2m 34s
	1h 10m 21s

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