enhance: doc parser support schema example

[amyXia1994]

Close #668

1. Does this PR affect any open issues?(Y/N) and add issue references (e.g. "fix #123", "re #123".):

• N
• Y

2. What is the scope of this PR (e.g. component or file name):

kclvm/api/src/service/ty.rs
kclvm/sema/src/resolver/doc.rs
kclvm/sema/src/resolver/global.rs
kclvm/sema/src/resolver/mod.rs
kclvm/sema/src/ty/mod.rs

kclvm/spec/gpyrpc/gpyrpc.proto

kclvm/api/src/testdata/get-schema-type-mapping.json
kclvm/api/src/testdata/get-schema-type-mapping.response.json
kclvm/sema/src/resolver/test_data/doc.k

3. Provide a description of the PR(e.g. more details, effects, motivations or doc link):

This PR support parsing the Examples section from the schema docstring, and exposes the examples field from the KclvmService.GetSchemaTypeMapping API

Note: The Example.value field of the KclvmService.GetSchemaTypeMapping API changed to string type.

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Other

4. Are there any breaking changes?(Y/N) and describe the breaking changes(e.g. more details, motivations or doc link):

• N
• Y

5. Are there test cases for these changes?(Y/N) select and add more details, references or doc links:

• Unit test
• Integration test
• Benchmark (add benchmark stats below)
• Manual test (add detailed scripts or steps below)
• Other

[amyXia1994]

@Peefy

I suggest to change the type of grpc.Example.value to String, since the example code snippet of the schema can only be represented in plain text. And currently, if we keep using prost_wkt_types::Any as the example value, the corresponding json representation of the Server schema's example in the kclvm/api/src/testdata/exec-program-with-include-schema-type-path.response.json file will be like:

{
    "@type":"type.googleapis.com/example.StringValue",
    "value":[109,121,67,117,115,116,111,109,65,112,112,32,61,32,65,112,112,67,111,110,102,105,103,117,114,97,116,105,111,110,32,123,10,32,32,32,32,110,97,109,101,32,61,32,34,99,111,109,112,111,110,101,110,116,78,97,109,101,34,10,125]
}
```, which is unreadable manually since the example value is wrapped and represented in bytes.

[Peefy]

LGTM