ref(browser): Extract global handlers private methods (#4265)

- Move private methods into regular functions as they don't use class
  props
- Use dynamic dispatch object, `_installFunc` to call install methods on instrumentation
- Extract capture exception into common method `function addMechanismAndCapture`
- Alias unminified variable names (remove `event.exception.values[0].stacktrace.frames`)
- Extract logging into function `function globalHandlerLog`
- Introduce function to call `getCurrentHub` and return client options.

Author: AbhiPrasad