VST3: Avoid re-querying parameter count while initialising parameters

[tjwrona]

Summary

This changes the VST3 hosted-parameter initialisation loop to snapshot
IEditController::getParameterCount() once before enumerating parameters.

The existing code re-queries getParameterCount() in the loop condition while constructing
VST3Parameter wrappers and fetching parameter info. We saw Neural DSP's
Archetype Gojira X.vst3 fail to instantiate through JUCE's VST3 hosting path until this count was
made stable for the initialisation pass.

getAllParamIDs() already follows the same snapshot-before-iteration pattern nearby.

Related issue: #1659

Testing

• Ran git diff --check
• Verified the local change fixes loading Archetype Gojira X.vst3 in the downstream host

[tjwrona]

Note that this patch seemed to also noticeably reduce the plugin load time for other heavy Neural DSP plugins.

[reuk]

Thanks for reporting, a fix is available on the juce9 preview branch:

f8fa54b