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/path-with-outputs.hh

@@ -6,13 +6,14 @@
 
 namespace nix {
 
-/* This is a deprecated old type just for use by the old CLI, and older
-   versions of the RPC protocols. In new code don't use it; you want
-   `DerivedPath` instead.
-
-   `DerivedPath` is better because it handles more cases, and does so more
-   explicitly without devious punning tricks.
-*/
+/**
+ * This is a deprecated old type just for use by the old CLI, and older
+ * versions of the RPC protocols. In new code don't use it; you want
+ * `DerivedPath` instead.
+ *
+ * `DerivedPath` is better because it handles more cases, and does so more
+ * explicitly without devious punning tricks.
+ */
 struct StorePathWithOutputs
 {
     StorePath path;
@@ -31,9 +32,11 @@ std::pair<std::string_view, StringSet> parsePathWithOutputs(std::string_view s);
 
 class Store;
 
-/* Split a string specifying a derivation and a set of outputs
-   (/nix/store/hash-foo!out1,out2,...) into the derivation path
-   and the outputs. */
+/**
+ * Split a string specifying a derivation and a set of outputs
+ * (/nix/store/hash-foo!out1,out2,...) into the derivation path
+ * and the outputs.
+ */
 StorePathWithOutputs parsePathWithOutputs(const Store & store, std::string_view pathWithOutputs);
 
 StorePathWithOutputs followLinksToStorePathWithOutputs(const Store & store, std::string_view pathWithOutputs);