Add CLI option --stdin-path to provide a virtual file location for stdin

[adecker89]

Description

Fixes #1123

Add an optional CLI --stdin-path to provide a virtual file location for stdin. This allows for re-enabling the FilenameRule as well as supporting custom rules that rely on the file path while still using stdin.

Checklist

Before submitting the PR, please check following (checks which are not relevant may be ignored):

• Commit message are well written. In addition to a short title, the commit message also explain why a change is made.
• At least one commit message contains a reference Closes #<xxx> or Fixes #<xxx> (replace<xxx> with issue number)
• Tests are added
• KtLint format has been applied on source code itself and violations are fixed
• PR title is short and clear (it is used as description in the release changelog)
• PR description added (background information)

Documentation is updated. See difference between snapshot and release documentation

• Snapshot documentation in case documentation is to be released together with a code change
• Release documentation in case documentation is related to a released version of ktlint and has to be published as soon as the change is merged to master

[paul-dingemans]

Tnx for your contribution. I have made some fixes as that was easier compared to provide feedback review. Most important is that you (accidentally) introduced a breaking API change.