Update flow + "@flow strict"

[IvanGoncharov]

It's such a pain to not be able to function args inside arrow functions, but the new version of Flow introduced @flow strict that makes function arguments constant.
Since @flow strict don't rely on .flowconfig it shouldn't cause the problem described in #1157.

It's a huge DX improvement for me since I spend 5-10 minutes debugging every time Flow is not able to figure out the type of function argument.

[leebyron]

I merged in the new flow version, but we don't need to use strict pragmas since we're not using the strict linter yet. The new flow version now tracks const args, but doesn't enforce them like you can enable as a strict linter

[leebyron]

I was wrong - it seems the strict mode adds additional checks in addition to applying the linter

[IvanGoncharov]

@leebyron Thanks for merge.
Why did you revert this code:

graphql-js/src/type/introspection.js

Lines 467 to 476 in 5fe3926

	// Would prefer to use introspectionTypes.some(), however %checks needs
	// a simple expression.
	(type.name === __Schema.name ||
	type.name === __Directive.name ||
	type.name === __DirectiveLocation.name ||
	type.name === __Type.name ||
	type.name === __Field.name ||
	type.name === __InputValue.name ||
	type.name === __EnumValue.name ||
	type.name === __TypeKind.name)

It was introduced in #1160 because you reverted experimental.const_params=true:
https://github.com/graphql/graphql-js/pull/1160/files#diff-87c5e74dd1f7d923143e0eee611f598eR150
Or I'm missing something?