str collect => str join (#6531)

* Initialize join.rs as a copy of collect.rs

* Evolve StrCollect into StrJoin

* Replace 'str collect' with 'str join' everywhere

git ls-files | lines | par-each { |it| sed -i 's,str collect,str join,g' $it }

* Deprecate 'str collect'

* Revert "Deprecate 'str collect'"

This reverts commit 959d14203e.

* Change `str collect` help message to say that it is deprecated

We cannot remove `str collect` currently (i.e. via
`nu_protocol::ShellError::DeprecatedCommand` since a prominent project
uses the API:

b85542c31c/src/virtualenv/activation/nushell/activate.nu (L43)

crates/nu-command/tests/commands/skip/until.rs

@@ -36,7 +36,7 @@ fn condition_is_met() {
                 | lines
                 | skip 2
                 | str trim
-                | str collect (char nl)
+                | str join (char nl)
                 | from csv
                 | skip until "Chicken Collection" == "Red Chickens"
                 | skip 1

crates/nu-command/tests/commands/skip/while_.rs

@@ -36,7 +36,7 @@ fn condition_is_met() {
                 | lines
                 | skip 2
                 | str trim
-                | str collect (char nl)
+                | str join (char nl)
                 | from csv
                 | skip while "Chicken Collection" != "Red Chickens"
                 | skip 1