Add OnBefore event for approval insertion checks

[Darrick (darjoo)]

What & why

Extensions cannot currently skip journal insertion approval checks, even when approvals are not used. Add OnBeforePreventInsertRecIfOpenApprovalEntryExist(Variant: Variant; var IsHandled: Boolean) to Approvals Mgmt. before record conversion and approval checks. Subscribers can set IsHandled to bypass the procedure; otherwise, its existing logic is unchanged.

Linked work

Fixes microsoft/ALAppExtensions#29214

AB#606350

How I validated this

• I read the full diff and it contains only changes I intended.
• I built the affected app(s) locally with no new analyzer warnings.
• I ran the change in Business Central and confirmed it behaves as expected.
• I added or updated tests for the new behavior, or explained below why none are needed.

What I tested and the outcome (required — be specific: scenarios, commands, screenshots for UI changes)

• git diff --check passed.
• A PowerShell source-contract check confirmed the publisher signature, a local IsHandled initialized to false, and the handled exit before RecRef.GetTable. Removing the new guard and publisher reproduced the original source, confirming the existing approval logic was not changed.
• Build and Business Central runtime validation remain pending; no AL compiler or Docker command was available in this environment. No AL tests were added. The PR remains a draft pending those checks.

Risk & compatibility

Additive integration event. Existing approval and cancellation behavior is unchanged unless a subscriber explicitly handles the event. No schema, permission, or upgrade changes.