Use final fields in equals and hashCode of PathPatternRequestMatcher

[codingtim]

The equals and hashCode implementation of PathPatternRequestMatcher was altered in
#17337

The current implementation of PathPatternRequestMatcher has a non-final field RequestMatcher method.
A setter is present for this field and is used in the Builder.

It seems like a bad practice to use non-final fields inside the equals and hashCode implementation.

I suggest improving this: codingtim@2b5df1c

[jzheaux]

Sounds great, @codingtim, and good catch. Are you able to submit this as a PR?

[jzheaux]

Closing in favor of #17621