🖊️ Add support for boolean values

[boryanagoncharenko]

Fixes #5370 Adds support for boolean values with the following caveats:

• we support both true and True as correct boolean values. Since hedy is currently case sensitive, this PR uses a workaround to support both values and does not attempt to solve the case sensitivity issue.
• when printed, the boolean value will appear as a correct python value, e.g. True, regardless in which language it was originally written. In other words, the Bulgarian program {print} {true} will yield literally True. The problem cannot be solved with the existing mechanisms in Hedy, so a separate issue will be created to address the matter.
• highlighting is still work in progress

How to test In levels 15-18, try the following programs:

a is true
print a

a is true

while a = True
    print 1
    a = false

print 2

[mergify[bot]]

Thank you for contributing! Your pull request is now going on the merge train (choo choo! Do not click update from main anymore, and be sure to allow changes to be pushed to your fork).

[mergify[bot]]

Thank you for contributing! Your pull request is now going on the merge train (choo choo! Do not click update from main anymore, and be sure to allow changes to be pushed to your fork).