Have . and .. as completions when completing directories

[Tyriar]

. (and ..) are valid folders that we should provide as a completion for directories.

See pwsh support:

When there's a directory before it, .. is there with a trialing / or \:

[meganrogge]

Reverted this as it caused issues

[meganrogge]

Notes from the discussion with @Tyriar

• If it's a file completion, always include / at end ../ (since .. is invalid)

• If it's a directory completion, omit .. since that's valid

• Resource resolving should be done in the renderer, since we want to merge all provider requests

• | - ie. A command/global or file

  • Show . since it's a source alias
  • Show ../ since it wants a file - since this is a file, not a folder we should include the /

• .|

  • Should include all executable files, maybe needs to be a fig spec thing

• cd |

  • Show ./ prefix for all folders
  • Show . since it's a valid directory
    • Maybe cd spec can tell us not to include the cwd?
  • Show .. since it's a valid directory

• cd ../|

  • Show ../<alldirs>
  • Show ../../ since ../.. cannot be chained together

• cd ../.|

  • The provider should give identical completions to cd ../|

• cd ../src (exact folder match)

  • The provider should give identical completions to cd ../|

cd | and cd ./| should provide identical completions

eg.

cd ./s, escape to hide, ctrl+space to show, backspace*3 should still show all suggestions since they're valid from replacementIndex