support fp16 in qnn delegate

[cccclai]

Stack from ghstack (oldest at bottom):

• #3342
• -> #3341

Differential Revision: D56551020

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As of commit 29f25448a5de83a6892442b07f0e16a0919e55c8 with merge base 5b0030f5d96606dd13000ffc019e9063ccb87f13 (): :green_heart: Looks good so far! There are no failures yet. :green_heart:

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This pull request was exported from Phabricator. Differential Revision: D56551020