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/crypto.hh

@@ -12,8 +12,10 @@ struct Key
     std::string name;
     std::string key;
 
-    /* Construct Key from a string in the format
-       ‘<name>:<key-in-base64>’. */
+    /**
+     * Construct Key from a string in the format
+     * ‘<name>:<key-in-base64>’.
+     */
     Key(std::string_view s);
 
     std::string to_string() const;
@@ -29,7 +31,9 @@ struct SecretKey : Key
 {
     SecretKey(std::string_view s);
 
-    /* Return a detached signature of the given string. */
+    /**
+     * Return a detached signature of the given string.
+     */
     std::string signDetached(std::string_view s) const;
 
     PublicKey toPublicKey() const;
@@ -53,8 +57,10 @@ private:
 
 typedef std::map<std::string, PublicKey> PublicKeys;
 
-/* Return true iff ‘sig’ is a correct signature over ‘data’ using one
-   of the given public keys. */
+/**
+ * @return true iff ‘sig’ is a correct signature over ‘data’ using one
+ * of the given public keys.
+ */
 bool verifyDetached(const std::string & data, const std::string & sig,
     const PublicKeys & publicKeys);