AST: Rename getFullName -> getName on ValueDecl & MissingMemberDecl

[AnthonyLatsis]

Follow-up to #30606

Now that FuncDecl::getName and EnumElementDecl::getName have been replaced with ValueDecl::getBaseIdentifier, we can rename ValueDecl::getFullName to getName() and thereby address the targeted FIXME.

[AnthonyLatsis]

swiftlang/llvm-project#1107

@swift-ci please smoke test

[CodaFi]

(Oh, it's cross-repo, ignore me)

[jckarter]

Looks good, thanks for seeing this through @AnthonyLatsis! Since this is just a rename, and we wouldn't want to deal with churn merging across branches, we probably want this in the swift-5.3-branch too once it lands in master.

[AnthonyLatsis]

Since this is just a rename, and we wouldn't want to deal with churn merging across branches, we probably want this in the swift-5.3-branch too once it lands in master.

Makes sense. Do we have a relevant 5.3 branch in the llvm-project repo?

[AnthonyLatsis]

@jckarter Also, I need someone to shepherd the PRs for me since the change is cross-repo. Thanks!

[jckarter]

@AnthonyLatsis Sounds good! Pulling this into release/5.3 in the swift repo and swift/release/5.3 on the llvm-project repo should do the job for the 5.3 branch.