fix: method is case insensitive

[fcrozatier]

closes #13634 

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[yashpandit]

should we also include capitalized variations? I believe they are also valid?

Suggested change

	formmethod?: 'dialog' | 'get' | 'post' | 'DIALOG' | 'GET' | 'POST' | undefined | null;
	formmethod?: 'dialog' | 'get' | 'post' | 'DIALOG' | 'GET' | 'POST' | 'Dialog' | 'Get' | 'Post' | undefined | null;

[trueadm]

Are they that common though? Searching through github and it seems to only be lowercase or all uppercase that I can find.

[fcrozatier]

I think it is common practice to see lower case only or upper case only, and I wouldn't mind even having only one version for consistency. Otherwise auto-completion will look like a mess if we respect the case-insensitivity

[fcrozatier]

Actually do we really want this? I've just checked the spec and a whole bunch of attributes are actually case-insensitive

https://html.spec.whatwg.org/#case-sensitivity-of-selectors

We clearly don't want case-insensitivity in general, this would make auto-completion a nightmare. For consistency I think lowercase only would be better. But HTTP verbs are commonly written in uppercase also so an exception can make sense...

[dummdidumm]

Agree that if at all we should only do this for these as they are the only ones somewhat commonly being uppercased