Pull Request for Issue #18912 (comment) .

Summary of Changes

• Normalise the method name for both PHP and JS world!
• Add appropriate deprecation
• Proxy Joomla.JText.* to Joomla.Text.*

Testing Instructions

Apply PR
Got to Admin -> Global configuration
Open the browser's console
Copy paste:

• Joomla.JText._('ERROR') press enter you should see "Error"
• Joomla.Text._('ERROR') press enter you should see "Error"
• Joomla.JText.strings press enter you should see an object with all the available strings
• Joomla.Text.strings press enter you should see the same object with all the available strings as before
• Joomla.Text.load({TEST: "test"}) and press enter then Joomla.Text.strings and check that TEST is there
• Joomla.Text.load({TESTA: "testa"}) and press enter then Joomla.Text.strings and check that TESTA is there

Expected result

Everything works as usual

Actual result

Documentation Changes Required

There are a bunch of console warnings added to help 3RD PD move forward. There will be a section in the documentation that will cover all the changes for J4.0

@mbabker up to you...