RFR: 8307625: Redundant receiver null check in LibraryCallKit::generate_method_call [v2]

[Eric Nothum]

> The null_check_receiver() calls in generate_method_call are redundant as all callers of generate_method_call already perform this check. For future uses of generate_method_call a new assert is introduced that fails if the caller does not null check the receiver.
> Also generally null_check_receiver() should be combined with stopped(), which was not the case here.

Eric Nothum has updated the pull request incrementally with one additional commit since the last revision:

  8307625: moved declaration of t inside the assert to avoid dead code in the product version.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/14542/files
  - new: https://git.openjdk.org/jdk/pull/14542/files/a6292a6a..5763fde8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14542&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14542&range=00-01

  Stats: 4 lines in 1 file changed: 0 ins; 2 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/14542.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14542/head:pull/14542

PR: https://git.openjdk.org/jdk/pull/14542