dillon1000/react

Ensure <fbt> children are not independently memod

This is a Meta-ism, but adding it for now to unblock. We special-case the 
`<fbt>` element for translation purposes, and have a transform that requires the 
children of this element to be a limited subset of nodes. Notably, any dynamic 
translation values must appear as `<fbt:param>` children — we disallow 
identifiers as children of `<fbt>` nodes. 

This PR adds a new pass which finds `<fbt>` nodes and ensures their immediate 
operands are not independently memoized. Note that this still allows the values 
of `<fbt:param>` to be independently memoized, as demonstrated in the unit test.