Serialize overline

Fixes #4529

addons/xterm-addon-serialize/test/SerializeAddon.api.ts

@@ -220,6 +220,18 @@ describe('SerializeAddon', () => {
     assert.equal(await page.evaluate(`serializeAddon.serialize();`), lines.join('\r\n'));
   });
 
+  it('serialize all rows of content with overline', async () => {
+    const cols = 10;
+    const line = '+'.repeat(cols);
+    const lines: string[] = [
+      sgr(OVERLINED) + line,                   // Overlined
+      sgr(UNDERLINED) + line,                  // Overlined, Underlined
+      sgr(NORMAL) + line                       // Normal
+    ];
+    await writeSync(page, lines.join('\\r\\n'));
+    assert.equal(await page.evaluate(`serializeAddon.serialize();`), lines.join('\r\n'));
+  });
+
   it('serialize all rows of content with color16 and style separately', async function(): Promise<any> {
     const cols = 10;
     const line = '+'.repeat(cols);
@@ -601,6 +613,7 @@ const BLINK = '5';
 const INVERSE = '7';
 const INVISIBLE = '8';
 const STRIKETHROUGH = '9';
+const OVERLINED = '53';
 
 const NO_BOLD = '22';
 const NO_DIM = '22';
@@ -610,3 +623,4 @@ const NO_BLINK = '25';
 const NO_INVERSE = '27';
 const NO_INVISIBLE = '28';
 const NO_STRIKETHROUGH = '29';
+const NO_OVERLINED = '55';