[hidingmyname]

Fixes #13154

SpiffeUtil.loadTrustBundleFromFile used the trust_domains keys as they were. A key that isn't a valid SPIFFE trust domain name, like UPPER.example.com or invalid#character, loaded without an error but could never match a peer: the peer's trust domain always comes from SpiffeUtil.parse(), so it is valid and lower case. Handshakes from that domain later failed with "Spiffe Trust Map doesn't contain trust domain ...", which doesn't point at the file. The javadoc and gRFC A87 both say that an invalid entry makes the whole bundle map invalid.

This validates each key with the existing validateTrustDomain(), the same check parse() uses, so an invalid name now throws IllegalArgumentException like other invalid content in the file. grpc-go also rejects the whole file in this case. FileWatcherCertificateProvider already reports load errors through onError() and keeps the previous map on a reload, so it needs no change.

One behavior change: a file that contains an invalid key next to valid ones used to load, with the invalid entry silently unused. Now the whole file is rejected.

Added loadTrustBundleFromFileInvalidTrustDomainTest to SpiffeUtilTest, covering invalid#character and UPPER.example.com. It fails without the change and passes with it, on JDK 21 and on JDK 8. :grpc-core:test (1583 tests) and checkstyle pass, as do the io.grpc.xds.internal.security tests in :grpc-xds (745 tests), which use the bundle map.