Dotty

Fix pkg obj prefix of opaque tp ext meth #33158

Job	Run time
test	55m 36s
test_non_bootstrapped	0s
test_scala2_library_tasty	0s
test_windows_fast	59m 19s
MiMa	11m 45s
test_windows_full	0s
community_build_a	53m 43s
community_build_b	1h 33m 40s
community_build_c	1h 6m 31s
test_sbt	18m 25s
build-msi-package	0s
test_java8	0s
build-sdk-package / build	7m 37s
test-msi-package	0s
build-chocolatey-package / build	23s
test-chocolatey-package	0s
publish_nightly	0s
publish_release	0s
nightly_documentation	0s
open_issue_on_failure	0s
	6h 6m 59s

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