Warn if the same operand is on either side of the equality operator

[Ramkarthik]

Closes #4205

Based on the conversation in the comments thread of the mentioned issue, I have implemented this for variables, field access, and literals. I'm not sure about module selects. @giacomocavalieri Could you please share an example for module select? (I'm still fairly new to Gleam)

Currently, it only checks for the same operand. In the case of literals, it doesn't warn if the check is 1 == 2 (which is always false). Do we want to handle those cases? If yes, I will likely have to rename the Warning::EqualityOnSameOperands variant and change the warning title. Any equality check for literals on both sides of the operator is always going to be the same result, so maybe we want to warn?

This PR also doesn't handle gt, gte, lt, and lte for Int and Float literals (based on the discussion in the issue thread).

If there's a better way to phrase the warning (title, hint, etc), please let me know.

Currently, the warning message template is:

warning: Same operand on either side of the equality operator
   ┌─ /code/gleam/gleam/test/equality/src/equality.gleam:10:8
   │
10 │   case name == name {
   │        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ This will always be true

Not related: It looks like the person who added this particular changelog entry missed adding their name/link - 65d7bb5

[Ramkarthik]

My bad, I forgot to run rust fmt which is causing the ci/rustfmt check to fail. Since there will likely be suggested changes, I will combine this with the changes in the next commit.

[lpil]

Thank you! Please see my comment here #4205 (comment)