Fixed Content on Same Line as Math Block Indicator Getting Put At Start of Each Line Outside of a Blockquote for Inline Math for Moving Math Indicators to Their Own Lines

[pjkaufman]

Fixes #996

There was an issue where if you had inline math present with other content on the line, if it met the conditions for converting to a math block, it would copy over the content on the same line, but prior to the opening math blocks.

For example, a $$b$$ would become:

a 
a $$
a b
a $$

This was fixed by getting the start of the line as either whitespace or blockquote indicators.

Thus it now becomes

a
$$
b
$$

I also addressed the more complex blockquote scenario to properly get the blockquote indicators.

> Here is a math block: $$a$$

now becomes

> Here is a math block:
> $$
> a
> $$

The logic also tries to cleanup whitespace that was present between the opening math block indicator and the content on the same line.

For example,

Here is a math block             $$b$$

becomes

Here is a math block
$$
b
$$

Changes Made:

• Reworked the logic for moving math block indicators to remove whitespace that was between line content and the opening math block indicators
• Reworked the logic to make it handle more blockquote and regular markdown scenarios
• Added UTs for a couple scenarios to make sure it worked
• Moved regex to the regex helper file