[0.76] Re-add `RCTHermesInstance` constructor for compatibility

[tido64]

Target Branch(es)

0.76

Link to commit or PR to be picked

facebook/react-native#46453

Description

facebook/react-native#46314 introduced a breaking change, making it hard to maintain backwards compatibility elsewhere. This change re-introduces the constructor that takes two arguments.

[cortinico]

Picked, will land in 0.76.0 RC1 ✅