fix(react): prevent intra-word _ and * from rendering as emphasis

[rahulnits-sketch]

Brief Title

fix(react): prevent intra-word _ and * from rendering as emphasis in composer

Acceptance Criteria fulfillment

• Prevent intra-word _ and * delimiters from being parsed as italics or bold (e.g. my_file_name.js, foo_bar_baz)
• Ensure delimiters touching whitespace (e.g. 2 * 3 * 4) do not trigger emphasis
• Retain expected markdown behavior for valid bold/italic spans (e.g. _italic_, **bold**, (_italic_))
• All 10 workspace packages build successfully via yarn build

Fixes #1372

PR Test Details

Note: The PR will be ready for live testing at https://rocketchat.github.io/EmbeddedChat/pulls/pr-1375 after approval.

Test Matrix

Input	Before (Bug)	After (Fixed)
my_file_name.js	my<em>file</em>name.js	my_file_name.js
call foo_bar_baz() now	call foo<em>bar</em>baz() now	call foo_bar_baz() now
2 * 3 * 4 = 24	2 <em> 3 </em> 4 = 24	2 * 3 * 4 = 24
This is _italic_ text	This is <em>italic</em> text	This is <em>italic</em> text
This is **bold** text	This is <strong>bold</strong> text	This is <strong>bold</strong> text
(_italic_)	(<em>italic</em>)	(<em>italic</em>)

[CLAassistant]

All committers have signed the CLA.

[rahulnits-sketch]

Hi @Spiral-Memory,

I have updated the commit author to align with my signed CLA, so all checks (including the CLA assistant) are now passing green ✅.

The changes in contentEditableComposer.js have been tested against all intra-word edge cases and all 10 workspace packages compile cleanly via yarn build. Whenever you have a moment, I would appreciate your review and feedback. Thank you!