build: Use Cargo.lock included with the repo by default

This should fix some future problems with dependencies getting updated in a way that's unsupported by the build tools targeted by Squeekboard.

meson_options.txt

@@ -15,6 +15,10 @@ option('online',
        type: 'boolean', value: true,
        description: 'Pull packages from the internet while building, as opposed to a local regstry.')
        
+option('reset_lock',
+       type: 'boolean', value: true,
+       description: 'Resets Cargo.lock to the one found in the source repo. Does not affect builds with online == false.')
+       
 option('strict',
        type: 'boolean', value: true,
        description: 'Turn more warnings into errors')