Enable Indexed Access Types in Xplat

Summary:
Enable Flow's Indexed Access Types (https://flow.org/en/docs/types/indexed-access/) in Xplat.

These are a replacement for `$ElementType` and `$PropertyType`.

Changelog: [Internal]

Remove `$FlowFixMe[indexed-access-off]`: `flow --json | jq -r ".errors[].message[0].path" | sort | uniq | xargs sed -i '/indexed-access-off/ d'`
Suppress new errors: `~/fbsource/xplat/js/scripts/flow/tool add-comments ~/fbsource/xplat/js/RKJSModules/public/XPlatReact/FXDemoShared/ --all --comment "Automatically suppressed"`
Re-sign: `hg st -n | grep '\.js$' | xargs --no-run-if-empty grep -lE 'generated|partially-generated'| xargs -n 1 -P 8 ~/fbsource/tools/signedsource sign`

Reviewed By: yungsters

Differential Revision: D32142892

fbshipit-source-id: 442092c497232750c729125383c9f4edcefbb6b1

.flowconfig

@@ -30,7 +30,6 @@ flow/
 emoji=true
 
 exact_by_default=true
-indexed_access=false
 
 format.bracket_spacing=false
 

.flowconfig.android

@@ -30,7 +30,6 @@ flow/
 emoji=true
 
 exact_by_default=true
-indexed_access=false
 
 format.bracket_spacing=false