Wean schema subject quickpick off of getSubjects() / GET /schemas route

[jlrobins]

Summary of Changes

• schemaSubjectQuickPick(), the quickpick for schema registry subject names (i.e. when uploading a new or revised schema) now based off of GET /subjects route results as from the new ResourceLoader method. Respelling this was low-hanging fruit in revising all callers to getSchemas().
• Alas, being based only on subject names means we cannot pre-filter based on schema type anymore, so we lose an ounce of functionality when being driven by the 'evolve schema' codepath. If the user picks, say, a preexisting AVRO subject when trying to upload a protobuf schema, now we'll expose the schema registry-produced error message, whereas before we would never let them pick an existing AVRO subject when the upload contents smelled protobuf, and so on.
• Therefore schemaSubjectQuickPick() and chooseSubject() drop their schema type parameter.
• Furthermore realize that no caller to either chooseSubject() or schemaSubjectQuickPick() provides the defaultSubject parameter anymore (was legacy from the original "evolve schema" implementation that depended on metadata attached to the editor buffer), so get rid of it. Alas, we hardly knew ye.

Any additional details or context that should be provided?

• Closes Migrate schemaSubjectQuickPick() to use new ResourceLoader.getSubjects() #997

Pull request checklist

Please check if your PR fulfills the following (if applicable):

Tests

• Added new
• Updated existing
• Deleted existing

Other

• All new disposables (event listeners, views, channels, etc.) collected as for eventual cleanup?

• Does anything in this PR need to be mentioned in the user-facing CHANGELOG or README?
• Have you validated this change locally by packaging and installing the extension .vsix file?

  gulp clicktest

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• CHANGELOG.md: Evaluated as low risk

Comments suppressed due to low confidence (3)

src/quickpicks/schemas.ts:15

• The parameter 'defaultSubject' is no longer used and should be removed from the function signature.

defaultSubject: string | undefined = undefined,

src/commands/schemaUpload.ts:222

• The comment mentions 'schema type' which is no longer a parameter of the function. It should be updated to reflect the current function signature.

// using the given schema type. Will return "" if they want to create a new subject.

src/commands/schemaUpload.ts:222

• The comment mentions 'defaultSubject' which is no longer a parameter of the function. It should be updated to reflect the current function signature.

// using the given schema type. Will return "" if they want to create a new subject.

Copilot reviewed 5 out of 6 changed files in this pull request and generated no comments.

Files not reviewed (1)

• src/quickpicks/schemas.ts: Evaluated as low risk

[jlrobins]

The core change right here. Basing schemaSubjectQuickPick on top of loader.getSubjects(schemaRegistry) returning the sorted subject names instead of loader.getSchemasForRegistry(schemaRegistry) returning all the schema metadatas.

Copilot reviewed 5 out of 6 changed files in this pull request and generated no comments.

Files not reviewed (1)

• src/commands/schemaUpload.ts: Evaluated as low risk