Add a better way to reference files/directories for IntelliJ plugin

[vldF]

The only way to do so is to put @ to the chat, select file and find the right one. Possibly, there are multiple files with needed name. Also the list sorts bad and sometimes you need to scroll it. Modern IDEs (like IJ and VS Code based) are cool enough to navigate over millions of files and developers are familiar with it.

Alternatively to #7000, this approach is to add a new context item to the file system viewer in IDEs which allows a user to reference the selected file in the chat

Possible feature extensions:

• Add a way to refer some elements in code like methods, classes, variables...
• Add a way to refer to some file with a prompt-based template

[vldF]

As far as I can see, this feature is present in VS Code https://docs.continue.dev/customize/deep-dives/vscode-actions

[aaudin90]

It is convenient to have the functionality of adding an open file from the editor.

As well as the ability to attach directories. But then there is a need to set up subdirectory ignores by mask or extensions, for example, so that generated folders such as build do not join.

[vldF]

CC @RomneyDa

[vldF]

I have sent this PR #7253. Now, for IJ plugin only