[CT-2961] Add flag to inform partial parsing to skip file diff computation

[MichelleArk]

In cloud environments, computing the file diff prior to partial parsing may be a costly operation. Provide a flag to skip computing a file diff that can be used to speed up parsing if the execution environment knows that no files have changed between dbt invocations.

[jtcohen6]

Let's hide the flag from the CLI --help text, since I think it will be confusing clutter for 99% of end users. Same as we did for #7911