Rollup merge of #67695 - gilescope:truth, r=centril
Rollup merge of #67695 - gilescope:truth, r=centril

Added dyn and true keyword docs

r? @Centril

aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust