Let 'rich' use code_theme as inline_code_theme

[tanavamsikrishna]

Problem

The inline code snippets in the reply from AI models are formatted using some default theme. They are somewhat harder to read and are just ugly.

Solution

Let the inline_code_theme as used in the rich.markdown.Markdown's __init__ have effect.

But if a inline_code_lexer is not passed to rich.markdown.Markdown, inline_code_theme is not being used to style inline code, as evident in the __init__ of rich.markdown.MarkdownContext. But there's no reasonably easy way to determine the programming language of inline code snippets to be able to identify the lexer. This PR's solution is to utilize the lexer text as the value of the inline_code_lexer passed to Markdown. In this scenario "rich" uses code_theme as the fallback value for inline_code_theme

[paul-gauthier]

Thanks!

[iamFIREcracker]

I was working on something similar: #4200