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/rotate.rs

@@ -25,7 +25,7 @@ fn counter_clockwise() {
         ]
         | where column0 == EXPECTED
         | get column1 column2 column3
-        | str collect "-"
+        | str join "-"
         "#,
     ));
 
@@ -35,7 +35,7 @@ fn counter_clockwise() {
             rotate --ccw
             | where column0 == EXPECTED
             | get column1 column2 column3
-            | str collect "-"
+            | str join "-"
         "#)));
 
     assert_eq!(actual.out, expected.out);
@@ -66,7 +66,7 @@ fn clockwise() {
         ]
         | where column3 == EXPECTED
         | get column0 column1 column2
-        | str collect "-"
+        | str join "-"
         "#,
     ));
 
@@ -76,7 +76,7 @@ fn clockwise() {
             rotate
             | where column3 == EXPECTED
             | get column0 column1 column2
-            | str collect "-"
+            | str join "-"
         "#)));
 
     assert_eq!(actual.out, expected.out);