Fix indentation in secret masking files (#5163)

`SecretMasker.cs` and `SecretMaskerL0.cs` have large portions indented to five spaces instead of four. This results in many `IDE055: Fix formatting` squiggles in VS. It is easy to fix these inadvertently while making other changes, which then makes reviewing those other changes more difficult.

This change was done using `Format Document (Ctrl+K, Ctrl+D)` in VS. It also fixed some instances of a missing space between attribute arguments.

Reviewing with the option to ignore whitespace should show no diff.

Co-authored-by: Nick Guerrera <[email protected]>

Author: merlynomsft