Add changelog entries for 2.0 release

[msujew]

In preparation for our 2.0 release, I've already added the changelog entries that contain the most important changes for adopters.

[montymxb]

The requested change is for one milestone link that needs to be corrected, but everything else looks good to go .

As a suggestion, here are all the additional items that I found tagged for the 1.3.0 milestone, but were not present in the changelogs. Not all may be relevant, so feel free to determine if/how we should include some of these:

• Use data instead of code for code actions #1128
• Infer optional properties for guarded groups #1116
• Use source maps for all debug configs #1114
• Improve regular expression generator #1109
• Add parser error message provider service #1108
• Check git status during CI #1098
• Use RootCstNode for root node property #1090
• Add support for regex flags #1070

However these couple for 1.3.0 are by external contributors, which would be good to include for recognition 🙂 .

• feat!: expose language metadata as const #1111
• Update document url in 'Cycle detected' error message #1057

[montymxb]

looks good!