fix(ui): the password prompt takes typing on Linux again (#2818)

The prompt's field requested focus on every frame. In egui 0.36 each
request also interrupts the input method, and egui-winit answers with
set_ime_allowed(false) then (true), which recreates the X11 input
context (or re-enables Wayland text-input) every frame. On Linux typed
keys go through the input method, so nothing typed reached the field.

Request focus only when the field doesn't have it, as the command
search does (#1638). The permissions password prompt shares the box.

Tests type through synthetic IME pre-edits and commits after opening
an encrypted file from the command line, File > Open, the start page
and a drop, and into the permissions prompt; both fail without the fix.

parity/acrobat-features.toml

@@ -178,8 +178,8 @@ milestone = "M1"
 status = "shipped"
 commands = ["file.open"]
 tools = ["doc_open"]
-evidence = ["crates/ui-egui/tests/editing.rs::password_prompt_opens_and_security_tab_reports_the_details", "crates/crypt/src/tests.rs::empty_user_password_opens_without_asking", "crates/ui-egui/src/open_worker_tests.rs::a_chosen_tool_survives_wrong_password_retry_and_runs_after_unlock", "crates/ui-egui/src/open_worker_tests.rs::startup_intake_waits_for_local_authentication_and_keeps_its_own_background_password_prompt"]
-notes = ""
+evidence = ["crates/ui-egui/tests/editing.rs::password_prompt_opens_and_security_tab_reports_the_details", "crates/crypt/src/tests.rs::empty_user_password_opens_without_asking", "crates/ui-egui/src/open_worker_tests.rs::a_chosen_tool_survives_wrong_password_retry_and_runs_after_unlock", "crates/ui-egui/src/open_worker_tests.rs::startup_intake_waits_for_local_authentication_and_keeps_its_own_background_password_prompt", "crates/ui-egui/tests/pickers.rs::the_open_password_can_be_typed_through_an_input_method_however_the_file_is_opened"]
+notes = "the field takes typing through the platform input method, which typed keys go through on Linux, however the file was opened (#2818); checked with synthetic input-method events, not on a Linux desktop"
 
 [[feature]]
 id = "core.unicode-passwords"
@@ -202,7 +202,7 @@ milestone = "M1"
 status = "shipped"
 commands = ["protect.unlock"]
 tools = ["doc_open"]
-evidence = ["crates/engine/src/tests.rs::restricted_documents_refuse_changes_unless_opened_by_the_owner", "crates/engine/src/tests.rs::owner_password_of_older_revisions_opens_the_viewer_too", "crates/crypt/src/tests.rs::owner_authentication_recovers_the_user_password", "crates/engine/src/tests.rs::the_permissions_password_unlocks_an_open_document", "crates/ui-egui/tests/editing.rs::the_security_notice_unlocks_with_the_permissions_password", "crates/ui-egui/tests/editing.rs::remove_security_asks_for_the_permissions_password_first"]
+evidence = ["crates/engine/src/tests.rs::restricted_documents_refuse_changes_unless_opened_by_the_owner", "crates/engine/src/tests.rs::owner_password_of_older_revisions_opens_the_viewer_too", "crates/crypt/src/tests.rs::owner_authentication_recovers_the_user_password", "crates/engine/src/tests.rs::the_permissions_password_unlocks_an_open_document", "crates/ui-egui/tests/editing.rs::the_security_notice_unlocks_with_the_permissions_password", "crates/ui-egui/tests/editing.rs::remove_security_asks_for_the_permissions_password_first", "crates/ui-egui/tests/pickers.rs::the_permissions_password_can_be_typed_through_an_input_method"]
 notes = "at open (the password prompt takes either password), or after opening a restricted file that needed no password (#995, #1077): Unlock… on the security notice and in Properties ▸ Security, and changing security asks for it first. Not yet: an automation tool to unlock an open document (reopen with doc_open and the password instead)"
 
 [[feature]]