Remove use of the word "force" in describing ApplyImpulse methods

[ericdow]

Changes

Since the various ApplyImpulse functions apply a "pure" impulse (resulting in an instantaneous change in velocity), using the word "force" is misleading. A force must be applied over some finite time span to produce a velocity change, whereas an impulse is applied instantaneously. This has led to confusion among developers.

Checks

By submitting your pull request for review, you agree to the following:

• This contribution was created in whole or in part by me, and I have the right to submit it under the terms of this repository's open source licenses.
• I understand and agree that this contribution and a record of it are public, maintained indefinitely, and may be redistributed under the terms of this repository's open source licenses.
• To the best of my knowledge, all proposed changes are accurate.

[PrinceTybalt]

LGTM.
Thanks for this