Scan backticks in jsdoc as a single token less often

Previously, matching backticks in jsdoc would always be scanned as one
token to aid parsing incorrect jsdoc that uses backticks for parameter
names:

``js
/** @param {string} `nope`
 * @param {number} `not needed`
 */
```

However, this is wrong for code fences, which use triple backticks. This
fix parses a single backtick as a single token if it's immediately
followed by another backtick or by a newline. It retains the
questionable tokenisation of backticks-as-pairs in other cases, however.
A better fix might be to have the parser ignore backticks in jsdoc
instead.

Author: sandersn

src/compiler/scanner.ts

@@ -2093,12 +2093,14 @@ namespace ts {
                 case CharacterCodes.dot:
                     return token = SyntaxKind.DotToken;
                 case CharacterCodes.backtick:
-                    while (pos < end && text.charCodeAt(pos) !== CharacterCodes.backtick) {
+                    if (pos < end && text.charCodeAt(pos) !== CharacterCodes.backtick && text.charCodeAt(pos) !== CharacterCodes.carriageReturn && text.charCodeAt(pos) !== CharacterCodes.lineFeed) {
+                        while (pos < end && text.charCodeAt(pos) !== CharacterCodes.backtick) {
+                            pos++;
+                        }
+                        tokenValue = text.substring(tokenPos + 1, pos);
                         pos++;
+                        return token = SyntaxKind.NoSubstitutionTemplateLiteral;
                     }
-                    tokenValue = text.substring(tokenPos + 1, pos);
-                    pos++;
-                    return token = SyntaxKind.NoSubstitutionTemplateLiteral;
             }
 
             if (isIdentifierStart(ch, ScriptTarget.Latest)) {

tests/baselines/reference/quickInfoForJSDocCodefence.baseline

@@ -0,0 +1,57 @@
+[
+  {
+    "marker": {
+      "fileName": "/tests/cases/fourslash/quickInfoForJSDocCodefence.ts",
+      "position": 54
+    },
+    "quickInfo": {
+      "kind": "function",
+      "kindModifiers": "",
+      "textSpan": {
+        "start": 52,
+        "length": 3
+      },
+      "displayParts": [
+        {
+          "text": "function",
+          "kind": "keyword"
+        },
+        {
+          "text": " ",
+          "kind": "space"
+        },
+        {
+          "text": "foo",
+          "kind": "functionName"
+        },
+        {
+          "text": "(",
+          "kind": "punctuation"
+        },
+        {
+          "text": ")",
+          "kind": "punctuation"
+        },
+        {
+          "text": ":",
+          "kind": "punctuation"
+        },
+        {
+          "text": " ",
+          "kind": "space"
+        },
+        {
+          "text": "string",
+          "kind": "keyword"
+        }
+      ],
+      "documentation": [],
+      "tags": [
+        {
+          "name": "example",
+          "text": "```\n1 + 2\n```"
+        }
+      ]
+    }
+  }
+]

tests/cases/fourslash/quickInfoForJSDocCodefence.ts

@@ -0,0 +1,12 @@
+/// <reference path='fourslash.ts' />
+
+/////**
+//// * @example
+//// * ```
+//// * 1 + 2
+//// * ```
+//// */
+////function fo/*1*/o() {
+////    return '2';
+////}
+verify.baselineQuickInfo();