Specify the index command line arguments

[dbaeumer]

Especially around project dependency computation.

[dbaeumer]

I propose the following additional parameters for a LSIF tool:

• --impact: takes a list of files and outputs the projects that need LSIF re- computation.

--impact should also take a @filename argument to denote a file that lists the changed files, separated by a new line.

[dbaeumer]

@heejaechang @LukaszMendakiewicz @BertanAygun

We discussed this a long time ago and it is something I would like to add.

Does the above proposal make sense to you?