Add static analyzer to discourage use of panic() (#15075)

* Implement static analysis to prevent panics

* Add nopanic to nogo

* Fix violations and add exclusions

Fix violations and add exclusions for all

* Changelog fragment

* Use pass.Report instead of pass.Reportf

* Remove strings.ToLower for checking init method name

* Add exclusion for herumi init

* Move api/client/beacon template function to init and its own file

* Fix nopanic testcase

encoding/ssz/detect/fieldspec.go

@@ -35,7 +35,7 @@ func (f fieldType) Size() int {
 	case typeBytes4:
 		return 4
 	default:
-		panic("can't determine size for unrecognizedtype ")
+		panic("can't determine size for unrecognizedtype ") // lint:nopanic -- Impossible field type.
 	}
 }
 

encoding/ssz/merkleize.go

@@ -68,9 +68,10 @@ func Depth(v uint64) (out uint8) {
 }
 
 // Merkleize with log(N) space allocation
+// This method will panic when count > limit.
 func Merkleize(hasher Hasher, count, limit uint64, leaf func(i uint64) []byte) (out [32]byte) {
 	if count > limit {
-		panic("merkleizing list that is too large, over limit")
+		panic("merkleizing list that is too large, over limit") // lint:nopanic -- Panic is communicated in godoc commentary.
 	}
 	if limit == 0 {
 		return