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-command/tests/commands/filter.rs

@@ -14,5 +14,5 @@ fn filter_with_return_in_closure() {
     ));
 
     assert_eq!(actual.out, "[2, 4, 6, 8, 10]");
-    assert!(actual.err.is_empty());
+    assert!(actual.err.contains("deprecated"));
 }