convert 1 line match to 2 lines for readability
implement cloned for Option
Deprecate hashmap's find_copy and get_copy in favour of cloned and clone
fallout from deprecating find_copy and get_copy
auto merge of #18927 : areski/rust/pr-improve-option-match-readl, r=jakub-

**match** are much more easy to read when it's not in 1 single line
auto merge of #18914 : Gankro/rust/cloned, r=aturon

Part of #18424. r? @aturon 

[breaking-change]
Fix fallout from coercion removal
auto merge of #19027 : nick29581/rust/coercions-4, r=alexcrichton

The forwards compatible parts of #18645, rebased. Converts implicit coercions from `[T, ..n]` to `&[T]` into explicit references.