WiFiManagerParameter API Changes

[dmadison]

This PR makes some small API changes to the WiFiManagerParameter class to improve clarity, usability, and encapsulation:

Length to Max Length

• All length arguments have been changed to maxLength
• getValueLength() has been changed to getValueMaxLength()

When used as an argument, this refers to the max length of the form and the size of the internal buffer, not the length of the string passed as an argument as expected.

Similarly, the value returned is the max length of the form and the size of the internal buffer, not the length of the value stored.

The internal name (_length) has not been changed to maintain compatibility with user code, as it's exposed as a protected value. This should be changed in the next major version.

ID to Name

• getID() has been changed to getName()

In HTML forms, names and IDs are two different attributes. Although this value is applied to both, when submitted the form data corresponds to the name, not the ID. This causes confusion if we want the name and ID to differ, since we are currently calling the name the ID internally.

The internal name (_id) has not been changed to maintain compatibility with user code, as it's exposed as a protected value. This should be changed in the next major version.

Value Received Function

• Created a setValueReceived() function to receive data from the server

Currently the user can set the parameter value and max length via the setValue(const char *defaultValue, int maxLength) function, and in WiFiManager::doParamSave() the server sets the value directly to the buffer pointer using the existing max length.

This function provides a standardized way for the server (and any user code) to set a new value while respecting the existing max length value. This is also virtual, so derived parameter classes can intercept the received value and perform additional logic or sanitization if necessary.

WiFiManager friendship removed

There is no reason for the WiFiManager class to have a friendship with the parameter class. The internal calls have been replaced with the corresponding public functions and the friendship has been removed.

Incidental Bugfixes

• setValue() now checks if a max length argument is negative
• WiFiManagerParameter's destructor is now virtual

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Although PR contains API changes there should be no breaking changes. The few items marked deprecated should be removed on the next major release.

If this is merged, here are the changes to make on the next major release:

• WiFiManagerParameter::_length should be refactored to _maxLength
• WiFiManagerParameter::getValueLength() const should be removed
• WiFiManagerParameter::_id should be refactored to _name
• WiFiManagerParameter::getID() const should be removed

This is a reworked version of PR #1772 that will serve as a basis for other WiFiManagerParameter related PRs.