bug: sass-migrator not converting overridden default variables to `with` clauses.

[arikorn]

If overriding variables are in the current file, sass-migrator correctly moves the to @use...with...
but if the variable comes from an imported file, sass-migrator does not fix it.

Example: 3 files:

// _overrideme.scss
$white: #fff !default;

// _variables.scss
$white: #bbb;

// App.scss (top-level Sass file)
@import 'variables';
@import 'overrideme';
@debug "white: #{$white}"; // is #bbb (value in *_variables.scss* overrides default in *_overrideme.scss*)

Run: sass-migrator module --verbose --migrate-deps App.scss
output:

Migrating App.scss

Converted App.scss

// App.scss (top-level Sass file)
@use 'variables';
@use 'overrideme';
@debug "white: #{overrideme.$white}"; // should be #bbb <<<===but is #fff instead

Expected conversion (one possibility):

// App.scss (top-level Sass file)
@use 'variables';
@use 'overrideme' with ($white: variables.$white);
@debug "white: #{overrideme.$white}"; // should be #bbb

another possibility might be to move or copy @use 'overrideme' to _variables.scss and even make it @forward 'overrideme' with ($white: #bbb)
A simpler option might be to detect the problem and print out a warning that manual intervention is needed.
Or just print out a warning unconditionally...

Use-case: big projects that use @import to break up a single large scss file may have all app-level variables defined in a single subfile. In this case the "_overrideme.scss" file is actually an external toolkit such as CoreUI. The migration tool currently creates syntactically correct output, but the css formatting fails because of the missing overrides.