Finish converting existing comments for internal API docs (#8146)

* Finish converting existing comments for internal API docs

99% of this was just reformatting existing comments. Only two exceptions:

- Expanded upon `BuildResult::status` compat note

- Split up file-level `symbol-table.hh` doc comments to get
  per-definition docs

Also fixed a few whitespace goofs, turning leading tabs to spaces and
removing trailing spaces.

Picking up from #8133

* Fix two things from comments

* Use triple-backtick not indent for `dumpPath`

* Convert GNU-style `\`..'` quotes to markdown style in API docs

This will render correctly.

src/libstore/gc-store.hh

@@ -12,19 +12,20 @@ typedef std::unordered_map<StorePath, std::unordered_set<std::string>> Roots;
 
 struct GCOptions
 {
-    /* Garbage collector operation:
-
-       - `gcReturnLive': return the set of paths reachable from
-         (i.e. in the closure of) the roots.
-
-       - `gcReturnDead': return the set of paths not reachable from
-         the roots.
-
-       - `gcDeleteDead': actually delete the latter set.
-
-       - `gcDeleteSpecific': delete the paths listed in
-          `pathsToDelete', insofar as they are not reachable.
-    */
+    /**
+     * Garbage collector operation:
+     *
+     * - `gcReturnLive`: return the set of paths reachable from
+     *   (i.e. in the closure of) the roots.
+     *
+     * - `gcReturnDead`: return the set of paths not reachable from
+     *   the roots.
+     *
+     * - `gcDeleteDead`: actually delete the latter set.
+     *
+     * - `gcDeleteSpecific`: delete the paths listed in
+     *    `pathsToDelete`, insofar as they are not reachable.
+     */
     typedef enum {
         gcReturnLive,
         gcReturnDead,
@@ -34,28 +35,38 @@ struct GCOptions
 
     GCAction action{gcDeleteDead};
 
-    /* If `ignoreLiveness' is set, then reachability from the roots is
-       ignored (dangerous!).  However, the paths must still be
-       unreferenced *within* the store (i.e., there can be no other
-       store paths that depend on them). */
+    /**
+     * If `ignoreLiveness` is set, then reachability from the roots is
+     * ignored (dangerous!).  However, the paths must still be
+     * unreferenced *within* the store (i.e., there can be no other
+     * store paths that depend on them).
+     */
     bool ignoreLiveness{false};
 
-    /* For `gcDeleteSpecific', the paths to delete. */
+    /**
+     * For `gcDeleteSpecific`, the paths to delete.
+     */
     StorePathSet pathsToDelete;
 
-    /* Stop after at least `maxFreed' bytes have been freed. */
+    /**
+     * Stop after at least `maxFreed` bytes have been freed.
+     */
     uint64_t maxFreed{std::numeric_limits<uint64_t>::max()};
 };
 
 
 struct GCResults
 {
-    /* Depending on the action, the GC roots, or the paths that would
-       be or have been deleted. */
+    /**
+     * Depending on the action, the GC roots, or the paths that would
+     * be or have been deleted.
+     */
     PathSet paths;
 
-    /* For `gcReturnDead', `gcDeleteDead' and `gcDeleteSpecific', the
-       number of bytes that would be or was freed. */
+    /**
+     * For `gcReturnDead`, `gcDeleteDead` and `gcDeleteSpecific`, the
+     * number of bytes that would be or was freed.
+     */
     uint64_t bytesFreed = 0;
 };
 
@@ -64,21 +75,27 @@ struct GcStore : public virtual Store
 {
     inline static std::string operationName = "Garbage collection";
 
-    /* Add an indirect root, which is merely a symlink to `path' from
-       /nix/var/nix/gcroots/auto/<hash of `path'>.  `path' is supposed
-       to be a symlink to a store path.  The garbage collector will
-       automatically remove the indirect root when it finds that
-       `path' has disappeared. */
+    /**
+     * Add an indirect root, which is merely a symlink to `path` from
+     * `/nix/var/nix/gcroots/auto/<hash of path>`.  `path` is supposed
+     * to be a symlink to a store path.  The garbage collector will
+     * automatically remove the indirect root when it finds that
+     * `path` has disappeared.
+     */
     virtual void addIndirectRoot(const Path & path) = 0;
 
-    /* Find the roots of the garbage collector.  Each root is a pair
-       (link, storepath) where `link' is the path of the symlink
-       outside of the Nix store that point to `storePath'. If
-       'censor' is true, privacy-sensitive information about roots
-       found in /proc is censored. */
+    /**
+     * Find the roots of the garbage collector.  Each root is a pair
+     * `(link, storepath)` where `link` is the path of the symlink
+     * outside of the Nix store that point to `storePath`. If
+     * `censor` is true, privacy-sensitive information about roots
+     * found in `/proc` is censored.
+     */
     virtual Roots findRoots(bool censor) = 0;
 
-    /* Perform a garbage collection. */
+    /**
+     * Perform a garbage collection.
+     */
     virtual void collectGarbage(const GCOptions & options, GCResults & results) = 0;
 };