Rollup merge of #154174 - cyrgani:incomplete-mcp, r=JonathanBrouwer

allow `incomplete_features` in most UI tests

This PR allows the `incomplete_features` lint for all UI tests except for the three directories with the largest number of tests (`traits`, `specialization` and `const-generics`) triggering this lint to keep the size of this PR manageable. The remaining three directories will be handled in followup PRs.

Part of rust-lang/rust#154168.

Author: JonathanBrouwer