This commit introduces the following optimizations:

1. We return an empty array for text nodes in `getDirectives` because
Angular does not support attaching logic to them. This optimization
improves performance of `getDirectives` significantly because text nodes
often result in expensive calls to `loadLContext` since we can't resolve
it from a parent node.
1. `getDirectives` now calls `loadLContext` with second argument `false`
so it doesn't throw an error. This brings another significant
improvement because prevents the VM from deoptimizing calls.

BREAKING CHANGE:

Previously the `ng.getDirectives` function threw an error in case a
given DOM node had no Angular context associated with it (for example
if a function was called for a DOM element outside of an Angular app).
This behavior was inconsistent with other debugging utilities under `ng`
namespace, which handled this situation without raising an exception.
Now calling the `ng.getDirectives` function for such DOM nodes would
result in an empty array returned from that function.

PR Close #41525

This commit refactors the code to replace `loadLContext` with `getLContext` calls. The only difference between these two functions is that the `loadLContext` supports throwing an error in case `LContext` can not be found. The investigation performed in angular#41525 revealed that throwing while retrieving `LContext` might have undesirable performance implications, so we should avoid that to make sure there are no accidental perf regressions in other parts of code that used `loadLContext`. Moreover, in most of the places the `loadLContext` was already called in a mode that prevented an error from being thrown, so this refactoring should have no effect on the actual behavior.

This commit refactors the code to replace `loadLContext` with `getLContext` calls. The only difference between these two functions is that the `loadLContext` supports throwing an error in case `LContext` can not be found. The investigation performed in #41525 revealed that throwing while retrieving `LContext` might have undesirable performance implications, so we should avoid that to make sure there are no accidental perf regressions in other parts of code that used `loadLContext`. Moreover, in most of the places the `loadLContext` was already called in a mode that prevented an error from being thrown, so this refactoring should have no effect on the actual behavior.

PR Close #41606