Change _unstable_getSharedRooms to _unstable_getMutualRooms

[ShadowJonathan]

In accordance with changes to matrix-org/matrix-spec-proposals#2666, renaming from "shared" to "mutual".

This updates #1417
This blocks matrix-org/matrix-react-sdk#4897

Notes: Change _unstable_getSharedRooms to _unstable_getMutualRooms and update unstable URL.
Type: task

Signed-off-by: Jonathan de Jong <jonathan@automatia.nl>

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This change is marked as an internal change (Task), so will not be included in the changelog.

[codecov-commenter]

Codecov Report

Merging #2271 (02e423b) into develop (106f7be) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

@@             Coverage Diff             @@
##           develop    #2271      +/-   ##
===========================================
- Coverage    58.96%   58.95%   -0.02%     
===========================================
  Files           91       91              
  Lines        16326    16329       +3     
  Branches      3766     3767       +1     
===========================================
  Hits          9627     9627              
- Misses        6699     6702       +3     

Impacted Files	Coverage Δ
src/client.ts	38.10% <0.00%> (-0.05%)	⬇️

[turt2live]

note also that this sort of rename is not required in order for the MSC to pass the implementation check. The name of the feature is less important than the function of it.

[ShadowJonathan]

(Synapse (re)implementation will happen concurrently)

[turt2live]

Thanks!