Stabilize trace context in non-OTLP formats and define casing (#3909)

Closes
#3303

## Changes

From @tigrannajaryan in
#3303 (comment):

> I think the conclusion in
#3518
was that we keep the names. It has been a while and there is no new
evidence that we need to do something else so I suggest that we submit a
PR that declares
https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/compatibility/logging_trace_context.md
"Stable" and closes this issue.

This marks the specification for using `trace_id`, `span_id`, and
`trace_flags` in non-OTLP logging formats stable.

CHANGELOG.md

@@ -26,6 +26,9 @@ release.
 
 ### Compatibility
 
+- Define casing for hex-encoded IDs and mark the "Trace Context in non-OTLP Log Formats" specification stable.
+  ([#3909](https://github.com/open-telemetry/opentelemetry-specification/pull/3909))
+
 ### SDK Configuration
 
 ### Common

specification/compatibility/logging_trace_context.md

@@ -1,6 +1,6 @@
 # Trace Context in non-OTLP Log Formats
 
-**Status**: [Development](../document-status.md)
+**Status**: [Stable](../document-status.md)
 
 <details>
 <summary>Table of Contents</summary>
@@ -24,8 +24,8 @@ representing [trace context](../logs/data-model.md#trace-context-fields). This
 document defines how trace context should be recorded in non-OTLP Log Formats.
 To summarize, the following field names should be used in legacy formats:
 
-- "trace_id" for [TraceId](../logs/data-model.md#field-traceid), hex-encoded.
-- "span_id" for [SpanId](../logs/data-model.md#field-spanid), hex-encoded.
+- "trace_id" for [TraceId](../logs/data-model.md#field-traceid), lowercase and hex-encoded.
+- "span_id" for [SpanId](../logs/data-model.md#field-spanid), lowercase and hex-encoded.
 - "trace_flags" for [trace flags](../logs/data-model.md#field-traceflags), formatted
   according to W3C traceflags format.
 
@@ -39,7 +39,7 @@ Trace id, span id and traceflags SHOULD be recorded via SD-ID "opentelemetry".
 For example:
 
 ```
-[opentelemetry trace_id="102981ABCD2901" span_id="abcdef1010" trace_flags="01"]
+[opentelemetry trace_id="102981abcd2901" span_id="abcdef1010" trace_flags="01"]
 ```
 
 ### Plain Text Formats
@@ -48,7 +48,7 @@ The fields SHOULD be recorded according to the customary approach used for a
 particular format (e.g. field:value format for LTSV). For example:
 
 ```
-host:192.168.0.1<TAB>trace_id:102981ABCD2901<TAB>span_id:abcdef1010<TAB>time:[01/Jan/2010:10:11:23 -0400]<TAB>req:GET /health HTTP/1.0<TAB>status:200
+host:192.168.0.1<TAB>trace_id:102981abcd2901<TAB>span_id:abcdef1010<TAB>time:[01/Jan/2010:10:11:23 -0400]<TAB>req:GET /health HTTP/1.0<TAB>status:200
 ```
 
 ### JSON Formats
@@ -59,7 +59,7 @@ The fields SHOULD be recorded as top-level fields in the JSON structure. For exa
 {
   "timestamp":1581385157.14429,
   "body":"Incoming request",
-  "trace_id":"102981ABCD2901",
+  "trace_id":"102981abcd2901",
   "span_id":"abcdef1010"
 }
 ```