fix(mac): standardize interaction between OSK and physical keyboard

[sgschantz]

The OSK conforms to these rules:

1. The state of the physical keyboard modifier keys takes precedence over the OSK modifiers
   a. If an OSK modifier such as shift is unselected, but the shift key is held down, then the OSK will display the shift layer
   b. If an OSK modifier is selected, it is reset when the corresponding physical modifier is pressed or released
2. If the OSK is open with a modifier key selected, the modifier will be applied to a character key pressed with the physical keyboard
3. Selected modifiers from the OSK can be combined with physical modifier keys to display a different layer in the OSK. For example with Shift selected in the OSK, if a user holds down the Option/Alt key, the shift-alt layer will be displayed in the OSK
4. Closing the OSK resets the state of all its modifiers so that it has no effect on what is typed with the physical keyboard

Fixes #12584

User Testing

• TEST_OSK_RESETS_ON_CLOSE: OSK modifiers are cleared when the OSK window is closed

1. Install and run the Keyman build associated with this PR
2. Switch to the Khmer Angkor keyboard and open the OSK
3. Click with the mouse on the shift key of the OSK
4. Confirm that the 'T' key on the OSK displays 'ទ'
5. Click T on the OSK and confirm that the ouptut is 'ទ'
6. Close the OSK
7. Open the OSK and confirm that the shift key is no longer selected and that the 'T' key on the OSK displays 'ត'

• TEST_OSK_SHIFT_LAYER_AFFECTS_PHYSICAL_KEYBOARD: OSK shift key affects physical typing

1. Switch to the Khmer Angkor keyboard and open the OSK
2. Open a note in the Stickies app
3. Click with the mouse on the shift key of the OSK
4. Confirm that the 'T' key on the OSK displays 'ទ'
5. Type T on the physical keyboard and confirm that the ouptut is 'ទ'

• TEST_OSK_SHIFT_OPTION_LAYER_AFFECTS_PHYSICAL_KEYBOARD: OSK shift-alt keys affect physical typing

1. Switch to the Khmer Angkor keyboard and open the OSK
2. Open a note in the Stickies app
3. Click with the mouse on the shift and alt keys of the OSK
4. Confirm that the 'T' key on the OSK displays '᧤'
5. Type T on the physical keyboard and confirm that the ouptut is '᧤'

• TEST_OSK_OPTION_LAYER_AFFECTS_PHYSICAL_KEYBOARD: OSK alt key affects physical typing

1. Switch to the Khmer Angkor keyboard and open the OSK
2. Open a note in the Stickies app
3. Click with the mouse on the alt key of the OSK
4. Confirm that the 'T' key on the OSK displays 'ឨ'
5. Type T on the physical keyboard and confirm that the ouptut is 'ឨ'

[keymanapp-test-bot]

User Test Results

Test specification and instructions

• ✅ TEST_OSK_RESETS_ON_CLOSE (PASSED) (notes)
• ✅ TEST_OSK_SHIFT_LAYER_AFFECTS_PHYSICAL_KEYBOARD (PASSED) (notes)
• ✅ TEST_OSK_SHIFT_OPTION_LAYER_AFFECTS_PHYSICAL_KEYBOARD (PASSED) (notes)
• ✅ TEST_OSK_OPTION_LAYER_AFFECTS_PHYSICAL_KEYBOARD (PASSED) (notes)

Test Artifacts

• macOS
  • Keyman for macOS

[SabineSIL]

LGTM 😄

[dinakaranr]

Test Results

I tested this issue with the attached "Keyman 18.0.160-aplha-local" build on macOS Sonoma. I'm sharing my observation here.

Setup:
Installed the "Keyman 18.0.160-alpha-local" build.dmg" file
Installed the "Khmer_Angkor" keyboard.

• TEST_OSK_RESETS_ON_CLOSE (Passed):

1. Install the "Keyman-18.0.160.dmg file.
2. Open the "Configuration" dialog by clicking the keyman icon.
3. Change the keyboard from "English" to "Khmer Angkor" by clicking the keyman icon.
4. Open the OSK by clicking the keyman icon.
5. Click the shift key on OSK by using the mouse.
6. Verified that the 'T' key on the OSK displays 'ទ'
7. Open the Note app.
8. Click the "T" on the OSK. 
9. Verified that the output is 'ទ'
10. Close the OSK
11. Open the OSK
12. Verified that the shift key is no longer selected OSK 
13. Verified that the 'T' key on the OSK displays 'ត'
    It works well.

• TEST_OSK_SHIFT_LAYER_AFFECTS_PHYSICAL_KEYBOARD (Passed):

1. Change the keyboard from "English" to "Khmer Angkor" by clicking the keyman icon.
2. Open the OSK by clicking the keyman icon.
3. Open a note in the Stickies app
4. Click the shift key on OSK by using the mouse.
5. Verified that the 'T' key on the OSK displays 'ទ'
6. Type T on the physical keyboard
7. Verified that the output is 'ទ'
   It works well.

• TEST_OSK_SHIFT_OPTION_LAYER_AFFECTS_PHYSICAL_KEYBOARD (Passed):

1. Change the keyboard from "English" to "Khmer Angkor" by clicking the keyman icon.
2. Open the OSK by clicking the keyman icon.
3. Open a note in the Stickies app
4. Click the shift & alt keys on OSK by using the mouse.
5. Verified that the 'T' key on the OSK displays '᧤'
6. Type T on the physical keyboard.
7. Verified that the output is '᧤'
   It works great for me.

• TEST_OSK_OPTION_LAYER_AFFECTS_PHYSICAL_KEYBOARD (Passed):

1. Change the keyboard from "English" to "Khmer Angkor" by clicking the keyman icon.
2. Open the OSK by clicking the keyman icon.
3. Open a note in the Stickies app
4. Click the alt key on OSK by using the mouse.
5. Verified that the 'T' key on the OSK displays 'ឨ'
6. Type T on the physical keyboard
7. Verified that the output is 'ឨ'
   It works well. Thank you.

[keyman-server]

Changes in this pull request will be available for download in Keyman version 18.0.162-alpha