feat: support embed fonts

[Maxpsc]

Through the new API addFonts, support embedding fonts into .ppt file.

[ChillyBots]

[Rigorich]

As it pointed out in https://github.com/gitbrent/PptxGenJS/issues/176, PowerPoint convert TTF/OTF font to it's own format FntData. So, as I tested, this PR doesn't work with TTF/OTF directly (there's error when opening presentation), but works with .fntdata files extracted from created manually PPTX with embedded fonts. Sadly, it's impossible to "embed only used symbols" in advance. And also embedded fonts work only in PowerPoint (and Aspose.Slides)

But if you still want to embed full font using this PR, here's instruction:

1. Locally install font you want to embed
2. Create new PowerPoint Presentation
3. View - Slide Master - Fonts
4. Replace Heading/Body fonts with your font name
5. File - Options - Save - Embed fonts in the file - Embed all characters
6. Save presentation
7. Change file extension from .pptx to .zip
8. Open .zip - ppt - fonts
9. Copy this single .fntdata file outside of zip
10. Convert this file to base64 string using any online converter
11. Embed font using code below

    const fontBase64 = '...';
    fetch(`data:application/octet-stream;base64,${fontBase64}`)
    .then(res => res.blob())
    .then(blob =>
        this.presentation.addFont({
            typeface: 'My Font Name',
            fontBlob: blob,
        })
    );

12. Save your presentation using base64 after any timeout

    setTimeout(() =>
    this.presentation.write('base64')
        .then((data) => {
            // open index.html to get presentation
            const downloadLink = document.createElement('a');
            downloadLink.href = `data:application/octet-stream;base64,${data}`;
            downloadLink.download = `TEST - ${new Date().toISOString()}.pptx`;
            downloadLink.click();
        })
        .catch((err) => {
            console.error(err);
        })
    , 0);