query: Display definitions for duplicate files

[fstachura]

This commit modifies get_idents_defs so that definitions are duplicated for duplicate files - files with same id as other files (and therefore same contents), but different paths.

Fixes: #402

[tleb]

This is an LLM output. It looks valid to me and the commands have been tested, no hallucination there.

---

Identifier pages still drop the references and doc comments of duplicate
files — this PR fixes that for definitions only.

Elixir stores file contents deduplicated: byte-identical files share one
blob id, and files_this_version yields their (id, path) pairs
consecutively. The defs/refs/docs iterators are keyed by blob id, so once
they have answered for the first path, the following paths with the same id
read nothing. get_idents_defs() carries the previous definitions slice
over to duplicate paths (this PR's fix for definitions), but rBuf and
docBuf have no such carry-over: a duplicate file contributes definitions,
but zero references and doc comments.

EAGAIN shows references in six arch/*/bits/errno.h headers holding only
three distinct contents — one path per content is displayed:

⟩ # commit 4f14855
⟩ git checkout -q -f franek/fix-402

⟩ # change musl repo because it's inaccessible and fetch a single tag
⟩ git diff -U0 utils/index
diff --git a/utils/index b/utils/index
index 3298a87..6f7f15f 100755
--- a/utils/index
+++ b/utils/index
@@ -47 +47 @@ project_fetch() {
-    $git fetch --all --tags -j4
+    $git fetch --no-tags remote0 +refs/tags/v1.2.6:refs/tags/v1.2.6
@@ -128 +128 @@ add_default_remotes $1 $# $2 mesa https://gitlab.freedesktop.org/mesa/mesa.git
-add_default_remotes $1 $# $2 musl https://git.musl-libc.org/git/musl
+add_default_remotes $1 $# $2 musl https://github.com/kraj/musl.git

⟩ docker build -q -t elixir-repro -f docker/Dockerfile .
⟩ sudo rm -rf data/

⟩ docker run --rm -v ./data:/srv/elixir-data --entrypoint index \
  elixir-repro /srv/elixir-data musl
... indexes v1.2.6 ...

⟩ docker run -d --name lxr-t -p 8080:80 -v ./data:/srv/elixir-data elixir-repro
⟩ curl -s http://localhost:8080/musl/v1.2.6/A/ident/EAGAIN | \
    sed -n '/Referenced in/,/<\/ul>/p' | grep -oE 'arch/[a-z0-9]+/bits/errno.h' | sort -u
arch/generic/bits/errno.h
arch/mips/bits/errno.h
arch/powerpc/bits/errno.h

⟩ # => only 3 of 6, mips64/mipsn32/powerpc64 are missing

⟩ docker rm -f lxr-t

The bug is read-path: get_idents_defs() dedups per file_idx but only
carries prev_dbuf_slice over for duplicate files. This patch fixes it:

⟩ git apply ../pr409-1.patch
⟩ docker build -q -t elixir-repro -f docker/Dockerfile .
⟩ docker run -d --name lxr-t -p 8080:80 -v ./data:/srv/elixir-data elixir-repro
⟩ curl -s http://localhost:8080/musl/v1.2.6/A/ident/EAGAIN | \
    sed -n '/Referenced in/,/<\/ul>/p' | grep -oE 'arch/[a-z0-9]+/bits/errno.h' | sort -u
arch/generic/bits/errno.h
arch/mips/bits/errno.h
arch/mips64/bits/errno.h
arch/mipsn32/bits/errno.h
arch/powerpc/bits/errno.h
arch/powerpc64/bits/errno.h

⟩ # => all 6, same index, only the web app rebuilt

⟩ docker rm -f lxr-t
⟩ git checkout -q -f master

pr409-1.patch