[SOL] Create explicit sign extension instruction #294

Job	Run time
abi-dump-setup	1m 20s
Build lldb / Lit Tests (ubuntu-latest)	21m 53s
Build lldb / Lit Tests (windows-2019)	1m 53s
Build lldb / Lit Tests (macOS-latest)	18m 23s
Test llvm,clang,libclc / Lit Tests (ubuntu-latest)	46m 25s
Test llvm,clang,libclc / Lit Tests (windows-2019)	2m 7s
Test lld / Lit Tests (ubuntu-latest)	9m 37s
Test llvm,clang,libclc / Lit Tests (macOS-latest)	1h 7m 50s
Test lld / Lit Tests (windows-2019)	2m 36s
Test lld / Lit Tests (macOS-latest)	11m 1s
abi-dump (build-baseline)	32m 17s
abi-dump (build-latest)	33m 8s
abi-compare	30s
	4h 9m 0s

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