Fixed #3366: Exclude ACSF files from code sniffing.

[danepowell]

Fixes #3366

Changes proposed:

• Exclude ACSF-generated files from code sniffing. This doesn't fix the root cause of PHPCS is invoked inconsistently between blt validate and git pre-commit hooks #3366 but at least fixes the worst of the symptoms caused by the regression in Update to Drupal Coder 8.3.x. #3132

Steps to replicate the issue:

1. Create a new BLT project.
2. Initialize ACSF (blt acsf:init)
3. Try to commit the result. Note the error in PHPCS is invoked inconsistently between blt validate and git pre-commit hooks #3366.
4. Run blt validate. Note that it passes okay.

The problem here is both the error in #3 and the fact that there's a discrepancy between #3 and #4.

Steps to verify the solution:

Same steps as above, but verify that there is no error.

[mikemadison13]

@danepowell i think we should roll this back to 9.2.x and 9.x if they are using phpcs 3.x (i think 9.2.x is?)

[danepowell]

Definitely, I'll backport after/if we approve this.