Introduce `semgrep` #487

Job	Run time
Test - beta toolchain	20s
Test - stable toolchain	14s
no_std no alloc	3m 10s
Test 32-bit version	40s
no_std with alloc	51s
Test - 1.48.0 toolchain	3m 22s
Test - nightly toolchain	14s
Check for changes to the public API	1m 11s
Cross test	1m 19s
	11m 21s

Provide feedback