Unify & standardize the v1.3 changelog (#1102)

* Reference MSCs where MSCs were not being referenced.
* Alter language to appear consistent and from a single voice.
* Bundle and group various changes together (will affect the final changelog - the rendered one still doesn't bundle appropriately).
* Move entries to the spec area they are intended to be in.

changelogs/client_server/newsfragments/1003.clarification

@@ -1 +1 @@
-Adjust the OpenAPI specification so that the type `Flow information` is explicitly defined when the CS spec is rendered.
+Adjust the OpenAPI specification so that the type `Flow information` is explicitly defined when the client-server API is rendered.

changelogs/client_server/newsfragments/1059.clarification

@@ -1 +1 @@
-Fix room state 400 code error examples to match known error codes.
+Fix various typos throughout the specification.

changelogs/client_server/newsfragments/3681.clarification

@@ -1 +1 @@
-Fix broken syntax in Server Access Control Lists definition.
+Fix various typos throughout the specification.

changelogs/room_versions/newsfragments/1037.clarification

@@ -1,2 +1 @@
-Improve readability of definitions in the state resolution v2 algorithm.
-
+Improve readability and understanding of the state resolution algorithms.

changelogs/room_versions/newsfragments/1042.clarification

@@ -0,0 +1 @@
+Improve readability and understanding of the state resolution algorithms.

changelogs/room_versions/newsfragments/1043.clarification

@@ -1 +1 @@
-Adjust mathematical notation used in the description of state resolution to render better in browsers.
+Improve readability and understanding of the state resolution algorithms.

changelogs/room_versions/newsfragments/1050.clarification

@@ -1 +1 @@
-Add cross-references to PDU content definitions from the authorisation rules.
+Improve readability of the authorization rules.

changelogs/room_versions/newsfragments/1093.clarification

@@ -1 +1 @@
-Auth rules: clarify that the resident server must sign a restricted join event.
+For room versions 8, 9, and 10: clarify which homeserver is required to sign the join event.

changelogs/room_versions/newsfragments/3737.clarification

@@ -1 +1 @@
-Fix join membership auth rules when `join_rule` is `knock`.
+For room versions 7, 8, 9, and 10: fix join membership authorization rules when `join_rule` is `knock`.

changelogs/room_versions/newsfragments/3739.feature

@@ -1 +1 @@
-Update the default room version to 9.
+Update the default room version to 9 as per [MSC3589](https://github.com/matrix-org/matrix-spec-proposals/pull/3589).

changelogs/server_server/newsfragments/1038.clarification

@@ -1 +1 @@
-Fix origin server name in S2S Request Authentication example.
+Clarify the format for the Authorization header.

changelogs/server_server/newsfragments/1045.clarification

@@ -1 +1 @@
-Expand a little on what it means for a PDU to be valid when discussing checks on PDUs.
+Clarify what a "valid event" means when performing checks on a received PDU.

changelogs/server_server/newsfragments/1055.clarification

@@ -1 +1 @@
-Clarify that valid_until_ts is in milliseconds, like other timestamps used in Matrix
+Clarify that `valid_until_ts` is in milliseconds, like other timestamps used in Matrix.

changelogs/server_server/newsfragments/1067.feature

@@ -1 +1 @@
-Add a destination property to the Authorization header.
+Add a `destination` property to the Authorization header, as per [MSC3383](https://github.com/matrix-org/matrix-spec-proposals/pull/3383).

changelogs/server_server/newsfragments/1070.clarification

@@ -1 +1 @@
-Clarify that checks on PDUs should refer to the state _before_ an event.
+Clarify that checks on PDUs should refer to the state *before* an event.

changelogs/server_server/newsfragments/998.clarification

@@ -1 +1 @@
-Remove `origin` field from PDUs which exists on many but not all PDUs in practice and doesn't serve an actual purpose.
+Remove largely unused `origin` field from PDUs.