Saved filter key shortcuts: lowercase letters have shift modifier added

[svobs]

System and IINA version:

• macOS 12.6
• IINA 1.3.0 develop branch, commit 6da6a3f

Expected behavior:
If a saved filter has a key equivalent, it should only include Shift if the user specified it.

Actual behavior:
When a filter is saved, theShift modifier is added for both lowercase and uppercase letters.

Steps to reproduce:

1. Pick a lowercase letter which is easy to distinguish from its uppercase variant, like 't', and make sure you haven't already assigned it to a keybinding in the Preferences > Key Bindings table.
2. From the Video menu, select Video Filters...
3. Click the + button to create a new filter. A new dialog should open with options.
4. Leave Crop selected on the left. On the right, enter 200 for Width, and 200 for Height, and leave Origin X & Origin Y empty. Click Add.
5. The dialog should close, and the new filter should appear in the list, with a Save button. Click `Save'.
6. Enter a name for the new filter, like "Custom Crop", then click the blank area under Shortcut Key:. Type 't' (or your chosen lowercase key). It should appear in the box in uppercase. Click Add.
7. The filter should now appear in the list under Saved filters.
8. Now go back to the Video menu, and hover over Saved Video Filters. See that the key will appear with a shift symbol in front of it.
9. Open a video and type the lowercase letter. See that IINA beeps at you. Type it again holding down Shift. See that the filter is activated and the video is cropped.

How often does this happen?
Always, given that the key is a letter which can have an uppercase form.