Improve Flow coverage by reducing typecasts through `any`

There are many unnecessary typecasts through `any` which
break the Flow of types across the program.

It's more bulletproof to avoid lying to ourselves about types.

Also fixed sketchy null check where zero ID would be skipped:
```diff
-  } else if (selectedElementID) {
+  } else if (selectedElementID !== null) {
```

src/devtools/store.js

@@ -503,7 +503,7 @@ export default class Store extends EventEmitter {
     while (current != null) {
       if (current.parentID === 0) {
         const rendererID = this._rootIDToRendererID.get(current.id);
-        return rendererID == null ? null : ((rendererID: any): number);
+        return rendererID == null ? null : rendererID;
       } else {
         current = this._idToElement.get(current.parentID);
       }

src/devtools/views/Profiler/ChartNode.js

@@ -10,8 +10,8 @@ type Props = {|
   height: number,
   isDimmed?: boolean,
   label: string,
-  onClick: Function,
-  onDoubleClick?: Function,
+  onClick: (event: SyntheticMouseEvent<*>) => mixed,
+  onDoubleClick?: (event: SyntheticMouseEvent<*>) => mixed,
   placeLabelAboveNode?: boolean,
   width: number,
   x: number,

src/devtools/views/Profiler/CommitFlamegraphListItem.js

@@ -26,7 +26,7 @@ function CommitFlamegraphListItem({ data, index, style }: Props) {
   const { maxSelfDuration, rows } = chartData;
 
   const handleClick = useCallback(
-    (event: MouseEvent, id: number, name: string) => {
+    (event: SyntheticMouseEvent<*>, id: number, name: string) => {
       event.stopPropagation();
       selectFiber(id, name);
     },

src/devtools/views/Profiler/FilterModal.js

@@ -7,7 +7,7 @@ import { useModalDismissSignal } from '../hooks';
 import styles from './FilterModal.css';
 
 type Props = {|
-  dismissModal: Function,
+  dismissModal: () => void,
 |};
 
 export default function FilterModal({ dismissModal }: Props) {
@@ -19,8 +19,8 @@ export default function FilterModal({ dismissModal }: Props) {
   } = useContext(ProfilerContext);
 
   const handleNumberChange = useCallback(
-    ({ currentTarget }) => {
-      const newValue = parseFloat(currentTarget.value);
+    (event: SyntheticEvent<HTMLInputElement>) => {
+      const newValue = parseFloat(event.currentTarget.value);
       setMinCommitDuration(
         Number.isNaN(newValue) || newValue <= 0 ? 0 : newValue
       );
@@ -29,9 +29,10 @@ export default function FilterModal({ dismissModal }: Props) {
   );
 
   const handleEnabledChange = useCallback(
-    ({ currentTarget }) => {
-      setIsCommitFilterEnabled(currentTarget.checked);
-      if (currentTarget.checked) {
+    (event: SyntheticEvent<HTMLInputElement>) => {
+      const checked = event.currentTarget.checked;
+      setIsCommitFilterEnabled(checked);
+      if (checked) {
         if (inputRef.current !== null) {
           inputRef.current.focus();
         }

src/devtools/views/Profiler/ProfilerContext.js

@@ -114,19 +114,16 @@ function ProfilerContextController({ children }: Props) {
   let rootHasProfilingData = false;
   if (importedProfilingData !== null) {
     rootHasProfilingData = true;
-  } else if (selectedElementID) {
-    rendererID = store.getRendererIDForElement(
-      ((selectedElementID: any): number)
-    );
-    rootID = store.getRootIDForElement(((selectedElementID: any): number));
-    rootHasProfilingData = store.profilingOperations.has(
-      ((rootID: any): number)
-    );
+  } else if (selectedElementID !== null) {
+    rendererID = store.getRendererIDForElement(selectedElementID);
+    rootID = store.getRootIDForElement(selectedElementID);
+    rootHasProfilingData =
+      rootID === null ? false : store.profilingOperations.has(rootID);
   } else if (store.roots.length > 0) {
     // If no root is selected, assume the first root; many React apps are single root anyway.
     rootID = store.roots[0];
     rootHasProfilingData = store.profilingOperations.has(rootID);
-    rendererID = store.getRendererIDForElement(((rootID: any): number));
+    rendererID = store.getRendererIDForElement(rootID);
   }
 
   const startProfiling = useCallback(() => store.startProfiling(), [store]);

src/devtools/views/Profiler/utils.js

@@ -27,15 +27,16 @@ export const calculateSelfDuration = (
     return 0;
   }
 
-  let selfDuration = ((actualDurations.get(id): any): number);
   const node = nodes.get(id);
   if (node == null) {
     throw Error(`Could not find node with id "${id}" in commit tree`);
   }
 
+  let selfDuration = actualDurations.get(id) || 0;
+
   node.children.forEach(childID => {
     if (actualDurations.has(childID)) {
-      selfDuration -= ((actualDurations.get(childID): any): number);
+      selfDuration -= actualDurations.get(childID) || 0;
     }
   });
 

src/devtools/views/hooks.js

@@ -88,7 +88,7 @@ export function useLocalStorage<T>(
 
 export function useModalDismissSignal(
   modalRef: { current: HTMLDivElement | null },
-  dismissCallback: Function
+  dismissCallback: () => void
 ): void {
   useEffect(() => {
     if (modalRef.current === null) {