(core) Add our very own implementation of tokenfield (aka pillbox, tag list)

Summary:
- Supports auto-completion
- Supports various keyboard interactions to delete/select/copy-paste tokens
- Supports various mouse interactions to select and move tokens.
- Supports undo/redo while editing tokens.

Test Plan: stand-alone fixture and browser test verify the supported behaviors

Reviewers: paulfitz

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D2789

app/common/csvFormat.ts

@@ -0,0 +1,38 @@
+/**
+ * Simple utilities for escaping/quoting/parsing CSV data.
+ *
+ * This only supports the default Excel-like encoding, in which fields containing any separators
+ * or quotes get quoted (using '"'), and quotes get doubled.
+ *
+ * Quoting is also applied when values contain leading or trailing whitespace, and on parsing,
+ * leading or trailing whitespace in unquoted values is trimmed, so that "," or ", " may be used
+ * as a separator.
+ *
+ * This is intended for copy-pasting multi-choice values, where plain comma-separated text is the
+ * most user-friendly, and CSV encoding is used to ensure we can handle arbitrary values.
+ */
+
+// Encode a row. If {prettier: true} is set, separate output with ", ". Leading whitespace gets
+// encoded in any case.
+export function csvEncodeRow(values: string[], options: {prettier?: boolean} = {}): string {
+  return values.map(csvEncodeCell).join(options.prettier ? ", " : ",");
+}
+
+export function csvDecodeRow(text: string): string[] {
+  // Clever regexp from https://github.com/micnews/csv-line
+  const parts = text.split(/((?:(?:"[^"]*")|[^,])*)/);
+  const main = parts.filter((v, idx) => idx % 2).map(csvDecodeCell);
+  // The "delimiter" (odd-numbered parts) is our content. If it's not at the start/end, it means
+  // we have commas, and should include empty fields at those ends.
+  if (parts[0]) { main.unshift(""); }
+  if (parts[parts.length - 1]) { main.push(""); }
+  return main;
+}
+
+export function csvEncodeCell(value: string): string {
+  return /[,\r\n"]|^\s|\s$/.test(value) ? '"' + value.replace(/"/g, '""') + '"' : value;
+}
+
+export function csvDecodeCell(value: string): string {
+  return value.trim().replace(/^"|"$/g, '').replace(/""/g, '"');
+}