Retain decimal precision when exporting CSV

Using `Number.prototype.toLocaleString()` has the unexpected behavior of truncating anything
exceeding 3 decimal digits on floats.

Additionally, it introduces inconsistencies (comma vs period separators) which could make processing the
output CSV harder than it could be.  The proposed solution here is to simply let numbers be cast
automatically via string concatenation.

Fixes #13929

public/app/core/specs/file_export.test.ts

@@ -73,6 +73,7 @@ describe('file_export', () => {
         ],
         rows: [
           [123, 'some_string', 1.234, true],
+          [1000, 'some_string', 1.234567891, true],
           [0o765, 'some string with " in the middle', 1e-2, false],
           [0o765, 'some string with "" in the middle', 1e-2, false],
           [0o765, 'some string with """ in the middle', 1e-2, false],
@@ -89,6 +90,7 @@ describe('file_export', () => {
       const expectedText =
         '"integer_value";"string_value";"float_value";"boolean_value"\r\n' +
         '123;"some_string";1.234;true\r\n' +
+        '1000;"some_string";1.234567891;true\r\n' +
         '501;"some string with "" in the middle";0.01;false\r\n' +
         '501;"some string with """" in the middle";0.01;false\r\n' +
         '501;"some string with """""" in the middle";0.01;false\r\n' +

public/app/core/utils/file_export.ts

@@ -41,10 +41,8 @@ function formatSpecialHeader(useExcelHeader) {
 function formatRow(row, addEndRowDelimiter = true) {
   let text = '';
   for (let i = 0; i < row.length; i += 1) {
-    if (isBoolean(row[i]) || isNullOrUndefined(row[i])) {
+    if (isBoolean(row[i]) || isNumber(row[i]) || isNullOrUndefined(row[i])) {
       text += row[i];
-    } else if (isNumber(row[i])) {
-      text += row[i].toLocaleString();
     } else {
       text += `${QUOTE}${csvEscaped(htmlUnescaped(htmlDecoded(row[i])))}${QUOTE}`;
     }