Formatting removes leading special whitespace (U+2003)

Describe the bug

The formatter removes both leading and trailing special whitespace characters (e.g. U+2003).

Let's say you have a YAML file containing leading special whitespace (U+2003):

some_string: "a
   b  # this line starts with 2 spaces for indentation followed by an U+2003
  \u2003c"  # here's an explicit U+2003

Expected Behavior

I would like to keep all leading (and trailing) special whitespace characters.

Current Behavior

Applying the formatter yields:

some_string: "a
  b  # this line starts with 2 space for indentation; the U+2003 HAS BEEN REMOVED
  \u2003c" # here still is an explicit U+2003

Environment

• Windows
• Mac
• Linux
• other (please specify)

Start by running the formatter on the YAML example containing U+2003 and compare the output with the expected behavior described in the issue. Trace the formatter entry point used for YAML files; done means leading and trailing special whitespace is preserved while ordinary indentation and the explicit escape remain unchanged.