Add Flag to disable global text measure cache

[NickGerleman]

Summary: Facsimile may or may not use a global measure cache. Adding flags to let us run experiment, to understand real-world performance impact, now that we have fixed some (but not all) of the issues which may lead to measurement invalidation in Fabric.

Also does some quick cleanup th SimpleThreadSafeCache to remove the cache key as part of the lambda, which is never used, and makes this change mildly less efficient, and to accept lambda by generic type instead of repacking into std::function which has runtime overhead.

Changelog: [Internal]

Differential Revision: D75509799

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D75509799

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D75509799

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D75509799

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D75509799

[facebook-github-bot]

This pull request has been merged in facebook/react-native@9478c27a69cd419bb66d1c1add5143e001d81b6f.

[react-native-bot]

This pull request was successfully merged by @NickGerleman in 9478c27a69cd419bb66d1c1add5143e001d81b6f

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