Improve IME area reporting and set IME area in `TextArea` #2413

Job	Run time
cargo check (aarch64-android)	26s
cargo check (msrv) (wasm32)	34s
cargo check (msrv) (windows-latest)	1m 21s
cargo clippy (windows-latest)	5m 13s
cargo check (msrv) (macos-latest)	33s
cargo clippy (macos-latest)	2m 44s
cargo clippy (wasm32)	1m 56s
cargo doc	1m 9s
cargo check (msrv) (ubuntu-latest)	1m 2s
cargo clippy (ubuntu-latest)	3m 18s
formatting	29s
Prime LFS Cache	10s
cargo test (wasm32)	19s
typos	12s
cargo test (windows-latest)	3m 57s
cargo test (macos-latest)	1m 44s
cargo test (ubuntu-latest)	3m 59s
	29m 6s

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