[BUG] Consider not using placeholder text as a label

[DaveTryon]

(This is split out from #1738)

From @delphinegilbert:

Hello,

An accessibility audit was performed on Accessibility Insights for Windows in our department and the following issue was found:

Description of issue

At the top of the screen, right under "Live Inspect", there is a search field. The instructions "Search by name and control type" are provided to users as placeholder text in the search field, which disappears when you start typing in.

Impact on users

This will especially impact users with cognitive challenges such as short term memory loss, but can potentially impact any type of users. Instructions for an input field should be present at all time as a label generally above or next to the field to allow users to keep referring to it while they fill out the input field.

Steps to reproduce

Launch the program, and dismiss the startup windows. Using your mouse, hover or click on any other window for the program to start inspecting. It should then display an item tree, there there's a search field at the top.