Linux/macOS: enable quick format for file containers

Allow normal file-hosted containers to use quick format in the Unix volume creation path by sizing the host file with ftruncate before backup headers are written.

Enable the GUI checkbox for normal file containers and honor --quick in text mode. Update the Unix HTML documentation for the weaker deniability properties of sparse or unwritten host regions.

doc/html/en/Command Line Usage for Unix.html

@@ -253,7 +253,7 @@
 </tr>
 <tr>
 <td><em>--quick</em></td>
-<td>Enable quick formatting when creating a volume. This option must not be used when creating an outer volume.</td>
+<td>Enable quick formatting when creating a normal file-hosted or device-hosted volume. Do not use this option when creating an outer volume. In text mode, VeraCrypt cannot infer that a normal volume is intended to become an outer volume. For file containers, Quick Format may create sparse or unwritten host regions. Allocation behavior depends on host filesystem sparse-file support, and later writes can fail if the host filesystem runs out of space.</td>
 </tr>
 <tr>
 <td><em>--random-source=FILE</em></td>
@@ -326,7 +326,7 @@
 <h4>Hidden Volume Creation in Text Mode</h4>
 <p>Inexperienced users should use the graphical user interface to create a hidden volume. When using the text user interface, the following procedure must be followed:</p>
 <ol>
-<li>Create an outer volume with no filesystem.</li>
+<li>Create an outer volume with no filesystem and without <em>--quick</em>.</li>
 <li>Create a hidden volume within the outer volume.</li>
 <li>Mount the outer volume using hidden volume protection.</li>
 <li>Create a filesystem on the virtual device of the outer volume.</li>