Fix conditional local var highlight

[v010maaa]

Motivation

Closes #2690

This PR address the issue where syntax highlighting was not applied to syntax that assigns variables within conditions, such as if (a=1).

Implementation

• Address the syntax highlighting for local variable assignments within the conditions of case, if, elsif, unless, until, and while statements.
• Arithmetic operations such as +=, -=, *=, /=, and %= are also supported in the same manner.

Statement	Supported	Example	Notes
case	✅	case (x = foo)	-
if	✅	if (x = foo)	-
elsif	✅	elsif (x = foo)	-
unless	✅	unless (x = foo)	-
until	✅	until (x = foo)	-
while	✅	while (x = foo)	-
for	❌	for i in (x = 1..10)	Not applicable; assignment in range not typical
begin	❌	begin (x = foo)	Not applicable; doesn't have a condition
rescue	❌	rescue (x = foo)	Assignment in rescue condition not supported
else	❌	else (x = foo)	-
ensure	❌	ensure (x = foo)	Not applicable; doesn't have a condition

Automated Tests

Added three cases to check if(i=1), if(i+=1) and if(i&&=1)

Manual Tests

AS-IS	TOBE

[v010maaa]

I have signed the CLA!

[vinistock]

This is great. Can we also add the other forms of assignment? This is adding regular assignment and assignment operator. We are missing local variable and assignment and local variable or assignment. E.g.:

if (a ||= something)
end

if (a &&= something)
end

[v010maaa]

if (a &&= something) case added
15710d7 6cfcc5b

[vinistock]

Thank you for the contribution!