(core) Small fixes in plugin API docs

Summary:
While adding `FetchSelectedOptions` in 4e67c679b2, I accidentally made `viewApi` become an undocumented variable, which is fixed here.

While I was at it, I also fixed other errors emitted by `./build-plugin-api.sh`.

Test Plan: Built changes in https://github.com/gristlabs/grist-help/pull/297

Reviewers: paulfitz

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D4155

app/plugin/CustomSectionAPI.ts

@@ -34,6 +34,10 @@ export interface ColumnToMap {
   strictType?: boolean,
 }
 
+/**
+ * Tells Grist what columns a Custom Widget expects and allows users to map between existing column names
+ * and those requested by the Custom Widget.
+ */
 export type ColumnsToMap = (string|ColumnToMap)[];
 
 /**
@@ -78,6 +82,9 @@ export interface WidgetColumnMap {
   [key: string]: string|string[]|null
 }
 
+/**
+ * Interface for the mapping of a custom widget.
+ */
 export interface CustomSectionAPI {
   /**
    * Initial request from a Custom Widget that wants to declare its requirements.

app/plugin/GristAPI.ts

@@ -113,7 +113,7 @@ export interface GristDocAPI {
   listTables(): Promise<string[]>;
 
   /**
-   * Returns a complete table of data as [[RowRecords]], including the
+   * Returns a complete table of data as [[GristData.RowRecords]], including the
    * 'id' column. Do not modify the returned arrays in-place, especially if used
    * directly (not over RPC).
    */

app/plugin/grist-plugin-api.ts

@@ -52,10 +52,11 @@ export const rpc: Rpc = new Rpc({logger: createRpcLogger()});
 export const api = rpc.getStub<GristAPI>(RPC_GRISTAPI_INTERFACE, checkers.GristAPI);
 export const coreDocApi = rpc.getStub<GristDocAPI>('GristDocAPI@grist', checkers.GristDocAPI);
 
+const viewApiStub = rpc.getStub<GristView>('GristView', checkers.GristView);
+
 /**
  * Interface for the records backing a custom widget.
  */
-const viewApiStub = rpc.getStub<GristView>('GristView', checkers.GristView);
 export const viewApi: GristView = {
   ...viewApiStub,
   // Decoded objects aren't fully preserved over the RPC channel, so decoding has to happen on this side.