Offcanvas as component (#29017)

* Add a new offcanvas component

* offcanvas.js: switch to string constants and `event.key`

* Remove unneeded code

* Sass optimizations

* Fixes

Make sure the element is hidden and not offscreen when inactive
fix close icon negative margins
Add content in right & bottom examples
Re-fix bottom offcanvas height not to cover all viewport

* Wording tweaks

* update tests and offcanvas class

* separate scrollbar functionality and use it in offcanvas

* Update .bundlewatch.config.json

* fix focus

* update btn-close / fix focus on close

* add aria-modal and role
return focus on trigger when offcanvas is closed
change body scrolling timings

* move common code to reusable functions

* add aria-labelledby

* Replace lorem ipsum text

* fix focus when offcanvas is closed

* updates

* revert modal, add tests for scrollbar

* show backdrop by default

* Update offcanvas.md

* Update offcanvas CSS to better match modals

- Add background-clip for borders
- Move from outline to border (less clever, more consistent)
- Add scss-docs in vars

* Revamp offcanvas docs

- Add static example to show and explain the components
- Split live examples and rename them
- Simplify example content
- Expand docs notes elsewhere
- Add sass docs

* Add .offcanvas-title instead of .modal-title

* Rename offcanvas example to offcanvas-navbar to reflect it's purpose

* labelledby references title and not header

* Add default shadow to offcanvas

* enable offcanvas-body to fill all the remaining wrapper area

* Be more descriptive, on Accessibility area

* remove redundant classes

* ensure in case of an already open offcanvas, not to open another one

* bring back backdrop|scroll combinations

* bring back toggling class

* refactor scrollbar method, plus tests

* add check if element is not full-width, according to #30621

* revert all in modal

* use documentElement innerWidth

* Rename classes to -start and -end

Also copyedit some docs wording

* omit some things on scrollbar

* PASS BrowserStack tests

-- IOS devices, Android devices and Browsers on Mac, hide scrollbar by default and appear it, only while scrolling.

* Rename '_handleClosing' to '_addEventListeners'

* change pipe usage to comma

* change Data.getData to Data.get

Co-authored-by: XhmikosR <xhmikosr@gmail.com>
Co-authored-by: Martijn Cuppens <martijn.cuppens@gmail.com>
Co-authored-by: Mark Otto <markdotto@gmail.com>

js/src/util/scrollbar.js

@@ -0,0 +1,70 @@
+/**
+ * --------------------------------------------------------------------------
+ * Bootstrap (v5.0.0-beta2): util/scrollBar.js
+ * Licensed under MIT (https://github.com/twbs/bootstrap/blob/main/LICENSE)
+ * --------------------------------------------------------------------------
+ */
+
+import SelectorEngine from '../dom/selector-engine'
+import Manipulator from '../dom/manipulator'
+
+const SELECTOR_FIXED_CONTENT = '.fixed-top, .fixed-bottom, .is-fixed'
+const SELECTOR_STICKY_CONTENT = '.sticky-top'
+
+const getWidth = () => {
+  // https://developer.mozilla.org/en-US/docs/Web/API/Window/innerWidth#usage_notes
+  const documentWidth = document.documentElement.clientWidth
+  return Math.abs(window.innerWidth - documentWidth)
+}
+
+const hide = (width = getWidth()) => {
+  document.body.style.overflow = 'hidden'
+  _setElementAttributes(SELECTOR_FIXED_CONTENT, 'paddingRight', calculatedValue => calculatedValue + width)
+  _setElementAttributes(SELECTOR_STICKY_CONTENT, 'marginRight', calculatedValue => calculatedValue - width)
+  _setElementAttributes('body', 'paddingRight', calculatedValue => calculatedValue + width)
+}
+
+const _setElementAttributes = (selector, styleProp, callback) => {
+  const scrollbarWidth = getWidth()
+  SelectorEngine.find(selector)
+    .forEach(element => {
+      if (element !== document.body && window.innerWidth > element.clientWidth + scrollbarWidth) {
+        return
+      }
+
+      const actualValue = element.style[styleProp]
+      const calculatedValue = window.getComputedStyle(element)[styleProp]
+      Manipulator.setDataAttribute(element, styleProp, actualValue)
+      element.style[styleProp] = callback(Number.parseFloat(calculatedValue)) + 'px'
+    })
+}
+
+const reset = () => {
+  document.body.style.overflow = 'auto'
+  _resetElementAttributes(SELECTOR_FIXED_CONTENT, 'paddingRight')
+  _resetElementAttributes(SELECTOR_STICKY_CONTENT, 'marginRight')
+  _resetElementAttributes('body', 'paddingRight')
+}
+
+const _resetElementAttributes = (selector, styleProp) => {
+  SelectorEngine.find(selector).forEach(element => {
+    const value = Manipulator.getDataAttribute(element, styleProp)
+    if (typeof value === 'undefined' && element === document.body) {
+      element.style.removeProperty(styleProp)
+    } else {
+      Manipulator.removeDataAttribute(element, styleProp)
+      element.style[styleProp] = value
+    }
+  })
+}
+
+const isBodyOverflowing = () => {
+  return getWidth() > 0
+}
+
+export {
+  getWidth,
+  hide,
+  isBodyOverflowing,
+  reset
+}