v7 fix: remove explicit readonly semantics from Calendar grid in office-ui-fabric-react package

[smhigley]

Slowly making this fix in every single version of Calendar 😅

Here's the PR for the same fix in the date-time package: #23990
here's the original PR in v8: #20324

This is the same fix, but in the office-ui-fabric-react Calendar component.

[msft-fluent-ui-bot]

It looks like this change to the 7.0 branch may not have been submitted to master yet. Now that version 8 has released, all changes must be submitted to the master branch first (except in emergencies or if the change is irrelevant to version 8).

Please do one of the following:

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[codesandbox-ci]

This pull request is automatically built and testable in CodeSandbox.

To see build info of the built libraries, click here or the icon next to each commit SHA.

Latest deployment of this branch, based on commit 4e8f644:

Sandbox	Source
Fluent UI Button	Configuration
codesandbox-react-template	Configuration

[size-auditor]

Asset size changes

Project	Bundle	Baseline Size	New Size	Difference
office-ui-fabric-react	office-ui-fabric-react-Calendar	140.438 kB	140.415 kB	-23 bytes
office-ui-fabric-react	office-ui-fabric-react-DatePicker	208.512 kB	208.489 kB	-23 bytes

 Over Tolerance (1024 B)  Over Baseline  Below Baseline  New   Removed 1 kB = 1000 B

Baseline commit: f97b6b1eceee6656e2413a865ed9d9ef0c319df8 (build)

[fabricteam]

Perf Analysis

No significant results to display.

All results

Scenario	Render type	7.0 Ticks	PR Ticks	Iterations	Status
BaseButton	mount	768	768	5000
Breadcrumb	mount	36840	36877	5000
Checkbox	mount	1335	1263	5000
CheckboxBase	mount	1079	1112	5000
ChoiceGroup	mount	4186	4162	5000
ComboBox	mount	757	777	1000
CommandBar	mount	6838	6959	1000
ContextualMenu	mount	14934	14067	1000
DefaultButton	mount	965	954	5000
DetailsRow	mount	3205	3175	5000
DetailsRowFast	mount	3216	3194	5000
DetailsRowNoStyles	mount	3054	3028	5000
Dialog	mount	1934	1946	1000
DocumentCardTitle	mount	1555	1567	1000
Dropdown	mount	2110	2065	5000
FocusTrapZone	mount	1477	1496	5000
FocusZone	mount	1551	1552	5000
IconButton	mount	1407	1472	5000
Label	mount	287	295	5000
Layer	mount	1643	1657	5000
Link	mount	374	378	5000
MenuButton	mount	1212	1264	5000
MessageBar	mount	1784	1756	5000
Nav	mount	2800	2693	1000
OverflowSet	mount	1214	1119	5000
Panel	mount	1251	1138	1000
Persona	mount	807	816	1000
Pivot	mount	1256	1243	1000
PrimaryButton	mount	1036	1102	5000
Rating	mount	6644	6710	5000
SearchBox	mount	1075	1094	5000
Shimmer	mount	2210	2192	5000
Slider	mount	1283	1283	5000
SpinButton	mount	4199	4321	5000
Spinner	mount	363	356	5000
SplitButton	mount	2695	2649	5000
Stack	mount	432	433	5000
StackWithIntrinsicChildren	mount	1448	1468	5000
StackWithTextChildren	mount	4009	4112	5000
SwatchColorPicker	mount	8732	8788	5000
TagPicker	mount	2461	2497	5000
TeachingBubble	mount	42703	43898	5000
Text	mount	367	369	5000
TextField	mount	1202	1150	5000
Toggle	mount	702	685	5000
button	mount	89	98	5000

does not apply