Modify regex in textToMarkdown functionality

[jaylalakiya]

Fixed Issues

$ Expensify/App#27445

Tests

Following tests are related to changes I made and I needed to modify them because that's the correct behaviour (to have space before in in the first test and before in in the second test.

1. expensify-common/__tests__/ExpensiMark-Markdown-test.js

   Lines 554 to 559 in 35bff86

   	test('Test html to heading1 markdown when h1 tag is in the beginning of the line', () => {
   	const testString = '<h1>heading1</h1> in the beginning of the line';
   	const resultString = '# heading1\n'
   	+ 'in the beginning of the line';
   	expect(parser.htmlToMarkdown(testString)).toBe(resultString);
   	});

2. expensify-common/__tests__/ExpensiMark-Markdown-test.js

   Lines 561 to 567 in 35bff86

   	test('Test html to heading1 markdown when h1 tags are in the middle of the line', () => {
   	const testString = 'this line has a <h1>heading1</h1> in the middle of the line';
   	const resultString = 'this line has a\n'
   	+ '# heading1\n'
   	+ 'in the middle of the line';
   	expect(parser.htmlToMarkdown(testString)).toBe(resultString);
   	});

QA

1. Open any chat
2. Type # sometext
someothertext
3. Send the message and it should preserve the whitespace before second line.
4. Now create another message with text # sometext
someothertext
5. Send the message and it should remove the whitespace before first line but it should preserve it in front of second line.

[github-actions]

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[jaylalakiya]

I have read the CLA Document and I hereby sign the CLA

[srikarparsi]

Hey @jaylalakiya, your proposal has to be accepted by @parasharrajat and an internal engineer before your PR can be reviewed.