FindOpenSSL: add target OpenSSL::applink to support OpenSSL's applink feature

Fixes: #20701
42 jobs for !4737 with master in 5 minutes and 9 seconds (queued for 2 seconds)
latest detached
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  Build
passed build:debian10-iwyu #4954869
linux docker build

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passed build:fedora31-sphinx #4954871
linux-3.17 linux docker build

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passed build:fedora31-tidy #4954870
linux docker build

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  External
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