feat: hover information for grind anchors

[leodemoura]

This PR implements hover information for grind anchors. Anchors are stable hash codes for referencing terms in the grind state. The anchors will be used when auto generating tactic scripts. The hover display the following information:

1- In the instantiate tactic, it displays the type of the theorem being instantiated.

2- In the cases tactic, the hover information depends on the kind of case-split.
a) Proposition

b) A hypotheses. In this case, you can opt to replace the anchor with the hypothesis' name if it is accessible.

c) A term. The hover displays just the type, by grind logs a silent information with additional information