Fix PerfUnitTest Regression

We send the accessibilityWindowAttribute while inputmethod window
changes the layout to full-screen mode, which could slow the the
performance.

To fixt it, we cache the attributes in ViewRootImpl to avoid
unncessary IPC connection

Bug: 239288414
Test: use forrest to rerun the test
Change-Id: I158236d79df51678fd168dc988fe565793ef4a09