Explain why an MR suggestion is not applicable

Original Issue: #30707 (closed)

Based on this discussion > #30707 (comment 350407168), the issue is split up into 2 separate iterations.

In part 1, we will use a generic message for when the tooltip is disabled.

In part 2, we want to display the specific reason why the "Suggestion" button is disabled.

Example only (To be updated)

Case	Tooltip message (FE)	Note
source_branch_deleted: true	Can't apply as the source branch was deleted.
outdated: true	Can't apply as [this line was|these lines were] changed in a more recent version.
write_access: false	You don't have write access to the source branch.
different_content: false	This suggestion already matches its content.
merge_request_not_open	This merge request [is closed|was merged]. To apply this suggestion, edit this file directly.
Current user does not have Developer or higher role (to do in #224587 (closed))	N/A	Hide button.