[clangd] Don't ignore external HFI in SymbolCollector (llvm#88446)

The `FileEntry` corresponds to a `FileID` containing the
`SourceLocation` of a `NamedDecl` which (I think) might've been
deserialized from a PCM file. Considering external `HeaderFileInfo` here
is most likely the right thing to do here in order to get the correct
spelling in case the current compiler instance has not register this
file as a header yet.

(cherry picked from commit 95fbd8d)

Author: jansvoboda11

clang-tools-extra/clangd/index/SymbolCollector.cpp

@@ -440,7 +440,7 @@ class SymbolCollector::HeaderFileURICache {
     // Framework headers are spelled as <FrameworkName/Foo.h>, not
     // "path/FrameworkName.framework/Headers/Foo.h".
     auto &HS = PP->getHeaderSearchInfo();
-    if (const auto *HFI = HS.getExistingLocalFileInfo(*FE))
+    if (const auto *HFI = HS.getExistingFileInfo(*FE))
       if (!HFI->Framework.empty())
         if (auto Spelling =
                 getFrameworkHeaderIncludeSpelling(*FE, HFI->Framework, HS))