Landmark Role for accessibility

[mapengbo0314]

Describe the bug

This is more of an accessibility change, due to accessibility from W3, we should not use "landmark" as roles as it's an abstract role.

Should be a simple one line change for the role. These are the possible subclass roles,
banner
complementary
contentinfo
form
main
navigation
region
search

Minimal reproduction of the problem with instructions

Please see code in repo for calendar-open-day-event and search for "role="landmark"

Screenshots
In our accessibility check we found this issue.

Versions

• @angular/core: "^8.2.14"
• angular-calendar: 0.28.20 (2020-09-13)
• Browser name and version: Chrome Version 89.0.4389.128 (Official Build) (32-bit)

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