Map `fit-content-function` web feature

[howard-e]

Feature: "fit-content()" Reference: https://github.com/web-platform-dx/web-features/blob/main/features/fit-content-function.yml

Notable exclusions (all include equally tested sizing attributes):

• css/css-sizing/parsing/width-valid.html
• css/css-sizing/parsing/height-valid.html
• css/css-sizing/parsing/max-height-computed.html
• css/css-sizing/parsing/max-height-valid.html
• css/css-sizing/parsing/max-width-computed.html
• css/css-sizing/parsing/max-width-valid.html
• css/css-sizing/parsing/min-height-computed.html
• css/css-sizing/parsing/min-height-valid.html
• css/css-sizing/parsing/min-width-computed.html
• css/css-sizing/parsing/min-width-valid.html

[jcscottiii]

Please resolve conflicts @howard-e

[howard-e]

Please resolve conflicts @howard-e

@jcscottiii done! (along with some whitespace formatting to follow the other WEB_FEATURES.yml)