Update deprecation warnings (#15867)

# Description
- Use #15770 to
  - improve `get --sensitive` deprecation warning
  - add deprecation warning for `filter`
- refactor `filter` to use `where` as its implementation
- replace usages of `filter` with `where` in `std`

# User-Facing Changes
- `get --sensitive` will raise a warning only once, during parsing
whereas before it was raised during runtime for each usage.
- using `filter` will raise a deprecation warning, once

# Tests + Formatting
No existing test broke or required tweaking. Additional tests covering
this case was added.
- 🟢 toolkit fmt
- 🟢 toolkit clippy
- 🟢 toolkit test
- 🟢 toolkit test stdlib

# After Submitting
N/A

---------

Co-authored-by: Bahex <17417311+Bahex@users.noreply.github.com>

crates/nu-std/testing.nu

@@ -333,20 +333,20 @@ export def run-tests [
                 commands: (get-annotated $row.name)
             }
         }
-        | filter {|x| ($x.commands|length) > 0}
+        | where {|x| ($x.commands|length) > 0}
         | upsert commands {|module|
             $module.commands
             | create-test-record
         }
         | flatten
-        | filter {|x| ($x.test|length) > 0}
-        | filter {|x| if ($exclude_module|is-empty) {true} else {$x.name !~ $exclude_module}}
-        | filter {|x| if ($test|is-empty) {true} else {$x.test|any {|y| $y =~ $test}}}
-        | filter {|x| if ($module|is-empty) {true} else {$module == $x.name}}
+        | where {|x| ($x.test|length) > 0}
+        | where {|x| if ($exclude_module|is-empty) {true} else {$x.name !~ $exclude_module}}
+        | where {|x| if ($test|is-empty) {true} else {$x.test|any {|y| $y =~ $test}}}
+        | where {|x| if ($module|is-empty) {true} else {$module == $x.name}}
         | update test {|x|
             $x.test
-            | filter {|y| if ($test|is-empty) {true} else {$y =~ $test}}
-            | filter {|y| if ($exclude|is-empty) {true} else {$y !~ $exclude}}
+            | where {|y| if ($test|is-empty) {true} else {$y =~ $test}}
+            | where {|y| if ($exclude|is-empty) {true} else {$y !~ $exclude}}
         }
     )
     if $list {