#54972

Instead of having a generic `Retrigger` reason, add a new field on the `SignatureHelpContext` that tracks if this was a retrigger or not. This allows retrigger for all the different trigger reasons, including invoke.

Replace the old `Retriggger` trigger reason with `ContentChange` which tracks cursor movement and text updates.

This reverts commit fb1ed792.

This reverts commit 677234a7.

This reverts commit 217e29ad, reversing
changes made to 758206be.

To allow better code sharing between EH and search proc

Fixes #58357

Introduces the concept of a re-trigger character to the signature help provider. This is a seperate set of characters that are registered with the provider. Typing a retrigger character fires a new signature help request if signature help is already showing.

#54972

Fix for #51808.