fix: Text ignores special characters such as HTML tags

[shaohuzhang1]

fix: Text ignores special characters such as HTML tags --bug=1050847 --user=王孝刚 【应用】-文本转语音节点在接收到带有html标签或url的文本，生成的语音中没有忽略代码和url等信息 https://www.tapd.cn/57709429/s/1637065

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[shaohuzhang1]

The provided code includes several improvements and optimizations:

1. Function Separation: A new function _remove_empty_lines has been added to handle splitting and transcribing files separately, which improves modularity.

2. Markdown Conversion: The markdown_to_plain_text function uses Python's built-in re module to remove various Markdown elements such as images, links, headings, bold, italic, inline code, code blocks, unnecessary whitespace, HTML tags, and form renders. This greatly enhances the efficiency of text preprocessing for transcription tasks.

3. Regex Optimization: The regex patterns have been updated for better performance, especially those targeting multiple replacement operations.

4. Edge Case Handling: The code now handles edge cases such as tables rendered with <tbody>/<tr>/ by removing them using a regular expression (<tbody>[\s\S]*?</tbody>). Additionally, it ensures that the final text is stripped of leading and trailing spaces after processing.

Overall, these changes make the code more robust, efficient, and easier to maintain.