Rollup merge of #130670 - the8472:read-to-end-heuristics, r=ChrisDenton

delay uncapping the max_read_size in File::read_to_end

In rust-lang/rust#130600 (comment) I realized that we're likely still passing too-large buffers to the OS, at least once at the end.

Previous issues and PRs:
* #110650
* #110655
* #118222

r? ChrisDenton

Author: GuillaumeGomez