Find Text runs on main thread

Version and Platform (required):

• Binary Ninja Version: 3.0.3319-dev
• OS: macOS
• OS Version: 12.0.1

Bug Description:
When searching for text in the UI, the search runs on the main thread and waits for IL generation on the main thread. This causes the UI to lock up for larger files where IL generation can take many seconds per function.

Steps To Reproduce:
Please provide all steps required to reproduce the behavior:

1. Open any large binary. I'm using ntdll
2. Search for text in HLIL, I used "and rsp"
3. Observe monster lag spikes

Expected Behavior:
I expected the UI to continue being responsive while searching was in progress. The UI isn't modal so I did not expect it to hang the main thread waiting for results.

Additional Information:
MainWindow::findAll looks like it directly calls View::findAllText, which should probably be done instead in a background thread.

Start with MainWindow::findAll and View::findAllText, then reproduce the lag by searching for "and rsp" in HLIL on a large binary such as ntdll. Trace where IL generation and search work run, and verify that the UI remains responsive while results are produced in the background.