Add typing files for our translator libraries (#3175)

js/src/common/translator-icu-rich.d.ts

@@ -0,0 +1,26 @@
+declare module '@askvortsov/rich-icu-message-formatter' {
+  type IValues = Record<string, any>;
+
+  type ITypeHandler = (
+    value: string,
+    matches: string,
+    locale: string,
+    values: IValues,
+    format: (message: string, values: IValues) => string
+  ) => string;
+  type IRichHandler = (tag: any, values: IValues, contents: string) => any;
+
+  type ValueOrArray<T> = T | ValueOrArray<T>[];
+  type NestedStringArray = ValueOrArray<string>;
+
+  export class RichMessageFormatter {
+    locale: string | null;
+    constructor(locale: string | null, typeHandlers: Record<string, ITypeHandler>, richHandler: IRichHandler);
+
+    format(message: string, values: IValues): string;
+    process(message: string, values: IValues): NestedStringArray;
+    rich(message: string, values: IValues): NestedStringArray;
+  }
+
+  export function mithrilRichHandler(tag: any, values: IValues, contents: string): any;
+}

js/src/common/translator-icu.d.ts

@@ -0,0 +1,17 @@
+declare module '@ultraq/icu-message-formatter' {
+  export function pluralTypeHandler(
+    value: string,
+    matches: string,
+    locale: string,
+    values: Record<string, any>,
+    format: (text: string, values: Record<string, any>) => string
+  ): string;
+
+  export function selectTypeHandler(
+    value: string,
+    matches: string,
+    locale: string,
+    values: Record<string, any>,
+    format: (text: string, values: Record<string, any>) => string
+  ): string;
+}