Update Phpredis stubs to return false on failure

[kkmuffme]

Started in phpredis/phpredis#2120 (comment) - this PR adds false in additional methods

Makes mGet return type more detailed

Force values to be string, to avoid implicit cast creating hard to track bugs phpredis/phpredis#2015 (comment)

[orklah]

Didn't we had the official stub since last PR?

Is it incomplete still? Maybe it should be updated on their end first?

[kkmuffme]

Yes, the official stubs from a PR - that PR is merged to phpredis:develop now.

However the issues addressed here aren't fixed and will not get fixed in a long time, since phpredis' whole documentation needs to be updated too - this is really time consuming, so it won't be happening any time soon.
This PR addresses this issues for stubs though - it's the original stubs with false added to most (all?) methods that can return false.

See phpredis/phpredis#2154, phpredis/phpredis#1921, phpredis/phpredis#1923, ... - these pop-up every couple weeks/months for another function, so I applied "false" liberally: phpredis/phpredis#1921 (comment) phpredis/phpredis#2154 (comment)

[orklah]

ok fine but it's something we may have to revert if some user complain that some function can't return false and we can't find a case when it does