vrl: vrl: null and unicode escapes not working in string literals

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Problem

I recently found out that the null and unicode character escape sequences are not working in string literal expressions in VRL. The documentation makes sense, therefore I think something is off in the VRL parser.

Examples from the VRL REPL:

$ "hello\0world"
error[E202]: syntax error
  ┌─ :1:1
  │
1 │ "hello\0world"
  │ ^^^^^^^^^^^^^^ unexpected error: invalid escape character: \0
  │
  = see language documentation at https://vrl.dev

$ "hello\u{1F30E}world"  # also tested with \U{1F30E} and \u1F30E just in case
error[E202]: syntax error
  ┌─ :1:1
  │
1 │ "hello\u{1F30E}world"
  │ ^^^^^^^^^^^^^^^^^^^^^ unexpected error: invalid escape character: \u
  │
  = see language documentation at https://vrl.dev

All the other documented escape sequences seems to be working fine (although not all printed correctly):

$ "hello\nworld"
"hello\nworld"

$ "hello\"world"
"hello\"world"

$ "hello\'world"
"hello'world"

$ "hello\\world"
"hello\\world"

$ "hello\nworld"
"hello\nworld"

$ "hello\rworld"  # \r (carriage-return) was rendered instead of printed with an escape
world"

$ "hello\tworld"  # \t (tab) was rendered instead of printed with an escape
"hello  world"

Configuration

N/A

Version

vector 0.20.0 (x86_64-unknown-linux-gnu 2a706a3 2022-02-11)

Debug Output

No response

Example Data

No response

Additional Context

No response

References

No response