feat(datepicker): lit-flatpicker proof of concept (#600)

* add datepicker component

* Fix bug preventing all days to be enabled by default

* tweak to allow inline mode

* add vvd-umbrella dep

* update lit-flatpickr dep

* add month and week picker demo

* comments

* start porting over volta datepicker styles

* adjust flatpickr alt and mobile input to slot in vwc-textfield

* add clear functionality

* fix range mode styles

* add range container to datepicker

* add custom datepicker header

* remove comments

* update month and year on navigation

* apply Joella design comments

* use vwc-button for clear

* destroy flatpickr instance on component disconnect

* fix depcheck

* add core to datepicker

* style inline datepicker

* add closeOnSelect and disableMobile support

* comments

* add custom month view

* highlight selected month in month view

* design alignment

* style lint

* add year navigation

* add month picker functionality

* fix lint warnings

* prettier

* disable months in month view when max date set

Co-authored-by: yinon <yinon@hotmail.com>

__snapshots__/datepicker.md

@@ -0,0 +1,11 @@
+# `datepicker`
+
+#### `should internal contents`
+
+```html
+<input class="flatpickr flatpickr-input lit-flatpickr">
+<slot>
+</slot>
+
+```
+

components/datepicker/.depcheckrc

@@ -0,0 +1 @@
+ignores: ["flatpickr", "lit-flatpickr", "@vonage/vvd-core", "@vonage/vwc-datepicker", "@open-wc/*"]

components/datepicker/package.json

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+{
+	"name": "@vonage/vwc-datepicker",
+	"version": "1.2.0",
+	"description": "Datepicker component",
+	"homepage": "https://github.com/Vonage/vivid/tree/master/components/datepicker#readme",
+	"license": "ISC",
+	"main": "vwc-datepicker.js",
+	"module": "vwc-datepicker.js",
+	"files": [
+		"*.js",
+		"*.ts",
+		"*.map"
+	],
+	"repository": {
+		"type": "git",
+		"url": "https://github.com/vonage/vivid.git",
+		"directory": "components/datepicker"
+	},
+	"scripts": {
+		"test": "echo \"Error: run tests from root\" && exit 1",
+		"build:typescript": "tsc -b",
+		"build:styles": "umbrella-style-modules",
+		"build": "yarn run build:styles && yarn run build:typescript"
+	},
+	"bugs": {
+		"url": "https://github.com/Vonage/vivid/issues"
+	},
+	"dependencies": {
+		"@vonage/vvd-core": "^1.2.0",
+		"@vonage/vvd-foundation": "^1.2.0",
+		"@vonage/vwc-button": "^1.2.0",
+		"@vonage/vwc-icon-button": "^1.2.0",
+		"flatpickr": "^4.6.9",
+		"lit-flatpickr": "^0.2.5",
+		"lit-element": "^2.4.0",
+		"tslib": "^2.0.3"
+	},
+	"devDependencies": {
+		"@vonage/vvd-design-tokens": "^1.2.0",
+		"@vonage/vvd-typography": "^1.2.0",
+		"@vonage/vvd-umbrella": "^1.0.4",
+		"typescript": "^4.1.3"
+	}
+}