RFR: 7903132: Replace casts with type test pattern [v2]

[Ethan McCue]

> Replaces a handful of casts following type tests with the equivalent pattern syntax.
> 
> I cannot create a matching issue, as I do not have an account on the bug tracker.

Ethan McCue has updated the pull request incrementally with one additional commit since the last revision:

  Fix compile error with ClassSourceBuilder pattern

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Changes:
  - all: https://git.openjdk.java.net/jextract/pull/5/files
  - new: https://git.openjdk.java.net/jextract/pull/5/files/04247137..12c04e17

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jextract&pr=5&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jextract&pr=5&range=00-01

  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jextract/pull/5.diff
  Fetch: git fetch https://git.openjdk.java.net/jextract pull/5/head:pull/5

PR: https://git.openjdk.java.net/jextract/pull/5