feat(eslint-plugin): add rule prefer-optional-chain

[bradzacher]

Super straightforward implementation.
Didn't even need type information (just assumes the user has written type-correct code).

Will detect:

foo && foo.a && foo.a.b && foo.a.b.c;
foo && foo['a'] && foo['a'].b && foo['a'].b.c;
foo && foo.a && foo.a.b && foo.a.b.method && foo.a.b.method();

// this rule also supports converting chained strict nullish checks:
foo &&
  foo.a != null &&
  foo.a.b !== null &&
  foo.a.b.c != undefined &&
  foo.a.b.c.d !== undefined &&
  foo.a.b.c.d.e;

OFC provides a fixer, which will fix the above to:

foo?.a?.b?.c;
foo?.['a']?.b?.c;
foo?.a?.b?.method?.();

foo?.a?.b?.c?.d?.e;

[merlinnot]

Thank you for picking this up! Do you think it would be possible to handle on more pattern here?

a !== undefined && a.b !== undefined && a.b.c !== undefined

This is often used to alleviate the unsafety of &&.

[turadg]

Thanks for this!

User caveat: the fixer loses comments on the clipped ranges