Auto merge of #85815 - YuhanLiin:buf-read-data-left, r=m-ou-se

Add has_data_left() to BufRead

This is a continuation of #40747 and also addresses #40745. The problem with the previous PR was that it had "eof" in its method name. This PR uses a more descriptive method name, but I'm open to changing it.

diff --cc library/std/src/io/mod.rs
Simple merge

diff --cc library/std/src/io/tests.rs
Simple merge